MacLochlainns Weblog

This post is designed to illustrate PL/SQL code with techniques employed before Oracle Database 12c with manual sequence references rather than auto generated IDs. The trick is small but should be made with older code. It impacts creation statement, conditional drop statements, and modification to stored procedures that manage transactions across two or more tables.

The key to the difference is in the table creation. Prior to Oracle Database 12c, there were no automatic sequences that you could assign to table definitions. Tables were created without sequences, and sequences were created independently. Likewise, there was no “IF EXISTS” clause for a DROP statement, which meant conditional drops were required as anonymous blocks.

Old tables and sequences from the Oracle Database 11g would use the following definitions:

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/* Conditionally drop grandma table and grandma_s sequence. */
BEGIN
  FOR i IN (SELECT   object_name
            ,        object_type
            FROM     user_objects
            WHERE    object_name IN ('TWEETIE_BIRD','TWEETIE_BIRD_SEQ','GRANDMA','GRANDMA_SEQ')
            ORDER BY 1 DESC, 2) LOOP
    IF i.object_type = 'TABLE' THEN
      /* Use the cascade constraints to drop the dependent constraint. */
      EXECUTE IMMEDIATE 'DROP TABLE '||i.object_name||' CASCADE CONSTRAINTS';
    ELSE
      EXECUTE IMMEDIATE 'DROP SEQUENCE '||i.object_name;
    END IF;
  END LOOP;
END;
/
 
/* Create the table. */
CREATE TABLE GRANDMA
( grandma_id     NUMBER       CONSTRAINT grandma_nn1 NOT NULL
, grandma_house  VARCHAR2(30) CONSTRAINT grandma_nn2 NOT NULL
, CONSTRAINT grandma_pk       PRIMARY KEY (grandma_id)
);
 
/* Create the sequence. */
CREATE SEQUENCE grandma_seq;
 
/* Create the table with primary and foreign key out-of-line constraints. */
CREATE TABLE TWEETIE_BIRD
( tweetie_bird_id     NUMBER        CONSTRAINT tweetie_bird_nn1 NOT NULL
, tweetie_bird_house  VARCHAR2(30)  CONSTRAINT tweetie_bird_nn2 NOT NULL
, grandma_id          NUMBER        CONSTRAINT tweetie_bird_nn3 NOT NULL
, CONSTRAINT tweetie_bird_pk        PRIMARY KEY (tweetie_bird_id)
, CONSTRAINT tweetie_bird_fk        FOREIGN KEY (grandma_id)
  REFERENCES GRANDMA (GRANDMA_ID)
);
 
/* Create sequence. */
CREATE SEQUENCE tweetie_bird_seq;

The key to the differences in Oracle Database 12c are in the table creation, and then in the INSERT statement because you can exclude the surrogate key column. A surrogate key column is also known as an ID column or sequence identified column.

New tables and sequences from the Oracle Database 12c forward use the following definitions to manage sequences:

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/* Conditionally drop grandma table and grandma_s sequence. */
DROP TABLE IF EXISTS tweetie_bird;
DROP TABLE IF EXISTS grandma;
 
/* Create the table. */
CREATE TABLE GRANDMA
( grandma_id     NUMBER        DEFAULT grandma_seq.NEXTVAL
, grandma_house  VARCHAR2(30)  CONSTRAINT grandma_nn2 NOT NULL
, CONSTRAINT grandma_pk        PRIMARY KEY (grandma_id)
);
 
/* Create the table with primary and foreign key out-of-line constraints. */
CREATE TABLE TWEETIE_BIRD
( tweetie_bird_id     NUMBER        DEFAULT tweetie_bird_seq.NEXTVAL
, tweetie_bird_house  VARCHAR2(30)  CONSTRAINT tweetie_bird_nn1 NOT NULL
, grandma_id          NUMBER        DEFAULT grandma_seq.CURRVAL
, CONSTRAINT tweetie_bird_pk        PRIMARY KEY (tweetie_bird_id)
, CONSTRAINT tweetie_bird_fk        FOREIGN KEY (grandma_id)
  REFERENCES GRANDMA (GRANDMA_ID)
);

This is the pattern that I setup to explain the new default surrogate primary and foreign keys when I wrote the Oracle Database 12c PL/SQL Programming book (pp. 20-22). Unfortunately, it was just a simple example and fits this use case:

• You write one create_something procedure or function, also known interchangeably as a method, to insert initial records; and
• You write one add_something method add a subsequent dependent record; and

This is a common practice by many but it creates unnecessary code that you need to maintain, which translates to accumulated technical debt throughout a design. The technical debt grows by a factor of two when you want to overload behaviors for security features or batch processing.

A better solution is to write one method that accommodates both an creates a new record and adds dependent records. The warner_brother procedure will do that later in this post. To prepare for the warner_brother procedure the dependent tweetie_bird table needs to change.

The default of the .currval of a “parent” table’s sequence value is no longer guaranteed in an independent action. The create and add methods now share the same method, and inspection of an existing independent record is necessary for both the create and add methods.

The new tweetie_bird table looks like:

/* Create the table with primary and foreign key out-of-line constraints. */
CREATE TABLE TWEETIE_BIRD
( tweetie_bird_id     NUMBER        DEFAULT tweetie_bird_seq.NEXTVAL
, tweetie_bird_house  VARCHAR2(30)  CONSTRAINT tweetie_bird_nn1 NOT NULL
, grandma_id          NUMBER        CONSTRAINT tweetie_bird_nn2 NOT NULL
, CONSTRAINT tweetie_bird_pk        PRIMARY KEY (tweetie_bird_id)
, CONSTRAINT tweetie_bird_fk        FOREIGN KEY (grandma_id)
  REFERENCES GRANDMA (GRANDMA_ID)
);

The next part of the post discusses how to write the create and add procedure in pre-12c and 12c forward implementations. Clearly, the automatic generated sequence values are the best approach when you use user-defined names for them as shown earlier.

The warner_brother procedure models the idea that any grandma may have one or more Tweetie birds, which means you must check if there’s a row in the grandma table. If there’s a row in the grandma table, you shouldn’t insert a new row in the grandma table. The internal get_grandma_id function returns:

• A zero if there is no existing row in the grandma table. After which, the nested if-block will insert a new row into the grandma table; and then assign the grandma_seq.CURRVAL value to a local variable.
• An existing grandma_id value, which can be used as a foreign key value in the subsequent insert statement to the tweety_bird table.

The warner_brother procedure for Oracle Database 11g is shown below:

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/* Create or replace procedure warner_brother. */
CREATE OR REPLACE PROCEDURE warner_brother
  ( pv_grandma_house       VARCHAR2
  , pv_tweetie_bird_house  VARCHAR2 ) IS
 
  /* Declare a local variable for an existing grandma_id. */
  lv_grandma_id   NUMBER;
 
  FUNCTION get_grandma_id
  ( pv_grandma_house  VARCHAR2 ) RETURN NUMBER IS
 
    /* Initialized local return variable. */
    lv_retval  NUMBER := 0;  -- Default value is 0.
 
    /* A cursor that lookups up a grandma's ID by their name. */
    CURSOR find_grandma_id
    ( cv_grandma_house  VARCHAR2 ) IS
      SELECT grandma_id
      FROM   grandma
      WHERE  grandma_house = cv_grandma_house;
 
  BEGIN   
    /* Assign a grandma_id as the return value when a row exists. */
    FOR i IN find_grandma_id(pv_grandma_house) LOOP
      lv_retval := i.grandma_id;
    END LOOP;
 
    /* Return 0 when no row found and the grandma_id when a row is found. */
    RETURN lv_retval;
  END get_grandma_id;
 
BEGIN
 
  /* Set the savepoint. */
  SAVEPOINT starting;
 
  /*
   *  Identify whether a member account exists and assign it's value
   *  to a local variable.
   */
  lv_grandma_id := get_grandma_id(pv_grandma_house);
 
  /*
   *  Conditionally insert a new member account into the member table
   *  only when a member account does not exist.
   */
  IF lv_grandma_id = 0 THEN
 
    /* Insert grandma. */
    INSERT INTO grandma
    ( grandma_id
    , grandma_house )
    VALUES
    ( grandma_seq.NEXTVAL
    , pv_grandma_house );
    /* Assign grandma_seq.currval to local variable. */
    lv_grandma_id := grandma_seq.CURRVAL;
 
  END IF;
 
  /* Insert tweetie bird. */
  INSERT INTO tweetie_bird
  ( tweetie_bird_id
  , tweetie_bird_house 
  , grandma_id )
  VALUES
  ( tweetie_bird_seq.NEXTVAL
  , pv_tweetie_bird_house
  , lv_grandma_id );
 
  /* If the program gets here, both insert statements work. Commit it. */
  COMMIT;
 
EXCEPTION
  /* When anything is broken do this. */
  WHEN OTHERS THEN
    /* Until any partial results. */
    ROLLBACK TO starting;
END;
/

The warner_brother procedure for Oracle Database 12c forward simplifies somethings and complicates others. The DEFAULT for the grandma_id foreign key column in the tweetie_bird table must be overwritten with a copy of the correct primary key value. More or less, it requires the correct grandma_id column value by finding the existing row in the grandma table. The internal get_grandma_id function grabs that value while returning a value that precludes writing to the grandma table.

The warner_brother procedure for Oracle Database 12c forward shown below shows that the grandma_id column default value is overridden by a local lv_grandma_id value returned by the internal get_grandma_id function on lines 60 thru 65 below.

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/* Create or replace procedure warner_brother. */
CREATE OR REPLACE PROCEDURE warner_brother
  ( pv_grandma_house       VARCHAR2
  , pv_tweetie_bird_house  VARCHAR2 ) IS
 
  /* Declare a local variable for an existing grandma_id. */
  lv_grandma_id   NUMBER;
 
  FUNCTION get_grandma_id
  ( pv_grandma_house  VARCHAR2 ) RETURN NUMBER IS
 
    /* Initialized local return variable. */
    lv_retval  NUMBER := 0;  -- Default value is 0.
 
    /* A cursor that lookups up a grandma's ID by their name. */
    CURSOR find_grandma_id
    ( cv_grandma_house  VARCHAR2 ) IS
      SELECT grandma_id
      FROM   grandma
      WHERE  grandma_house = cv_grandma_house;
 
  BEGIN   
    /* Assign a grandma_id as the return value when a row exists. */
    FOR i IN find_grandma_id(pv_grandma_house) LOOP
      lv_retval := i.grandma_id;
    END LOOP;
 
    /* Return 0 when no row found and the grandma_id when a row is found. */
    RETURN lv_retval;
  END get_grandma_id;
 
BEGIN
 
  /* Set the savepoint. */
  SAVEPOINT starting;
 
  /*
   *  Identify whether a member account exists and assign it's value
   *  to a local variable.
   */
  lv_grandma_id := get_grandma_id(pv_grandma_house);
 
  /*
   *  Conditionally insert a new member account into the member table
   *  only when a member account does not exist.
   */
  IF lv_grandma_id = 0 THEN
 
    /* Insert grandma. */
    INSERT INTO grandma
    ( grandma_house )
    VALUES
    ( pv_grandma_house );
    /* Assign grandma_seq.currval to local variable. */
    lv_grandma_id := grandma_seq.CURRVAL;
 
  END IF;
 
  /* Insert tweetie bird. */
  INSERT INTO tweetie_bird
  ( tweetie_bird_house 
  , grandma_id )
  VALUES
  ( pv_tweetie_bird_house
  , lv_grandma_id );
 
  /* If the program gets here, both insert statements work. Commit it. */
  COMMIT;
 
EXCEPTION
  /* When anything is broken do this. */
  WHEN OTHERS THEN
    /* Until any partial results. */
    ROLLBACK TO starting;
END;
/

You can test either version with the following anonymous PL/SQL block:

/* Test the warner_brother procedure. */
BEGIN
  warner_brother( pv_grandma_house      => 'Yellow House'
                , pv_tweetie_bird_house => 'Cage');
  warner_brother( pv_grandma_house      => 'Yellow House'
                , pv_tweetie_bird_house => 'Tree House');
END;
/

Ultimately, we’ll use a natural join to test the integrity of primary and foreign key relationship:

/* Query results from warner_brother procedure. */
COL grandma_id          FORMAT 9999999  HEADING "Grandma|ID #"
COL grandma_house       FORMAT A20      HEADING "Grandma House"
COL tweetie_bird_id     FORMAT 9999999  HEADING "Tweetie|Bird ID"
COL tweetie_bird_house  FORMAT A20      HEADING "Tweetie Bird House"
SELECT *
FROM   grandma NATURAL JOIN tweetie_bird;

As always, I hope this helps those trying to leverage existing PL/SQL code into more modern code.

A standard approach using fall through in languages that support it, like C, C++, and Java leverages a case structure. Unfortunately, in language that follow the Pascal pattern case statements act like if-else-if-else statements. In the Pascal model, you need to use coupled loops.

PL/SQL follows that Pascal, via Ada, structure. So, you must couple the performance of the inner descending loop to the maximum value of the outer ascending loop. Here’s an example of how you would code that in PL/SQL with the 12 Days of Christmas song, which has a chorus that grows with each verse.

It requires the definition of two ADTs (Attribute Data Types), a UDT (User-Defined Data Type) like a struct(ure), and a UDT table of the UDT struct. They’re all done in this code snippet.

/* Create a list of strings. */
CREATE OR REPLACE
  TYPE days IS TABLE OF VARCHAR2(8);
/
 
/* Create a list of strings. */
CREATE OR REPLACE
  TYPE song IS TABLE OF VARCHAR2(36);
/
 
/* Create a record structure. */
CREATE OR REPLACE
  TYPE lyric IS OBJECT
  ( DAY  VARCHAR2(8)
  , gift VARCHAR2(24));
/
 
/* Create a list of the record structure. */
CREATE OR REPLACE
  TYPE lyrics IS TABLE OF LYRIC;
/

The twelve_days function that will display the lyrics of the 12-Days of Christmas. It reads forward through the 12 days of Christmas and backwards through the chorus in the inner loop beginning with the current day of the outer loop.

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/* Create a function. */
CREATE OR REPLACE
  FUNCTION twelve_days
  ( pv_days DAYS
  , pv_gifts LYRICS ) RETURN song IS
 
    /* Initialize the collection of lyrics. */
    lv_retval SONG := song();
 
    /* Local procedure to add to the song. */
    PROCEDURE ADD
    ( pv_input VARCHAR2 ) IS
    BEGIN
      lv_retval.EXTEND;
      lv_retval(lv_retval.COUNT) := pv_input;
    END ADD;
 
  BEGIN
    /* Read forward through the days. */
    FOR i IN 1..pv_days.COUNT LOOP
      ADD('On the ' || pv_days(i) || ' day of Christmas');
      ADD('my true love sent to me:');
 
      /* Read backward through the lyrics based on ascending value of the day. */
      FOR j IN REVERSE 1..i LOOP
        IF i = 1 THEN
          ADD('- '||'A'||' '||pv_gifts(j).gift);
        ELSE
          ADD('- '||pv_gifts(j).DAY||' '||pv_gifts(j).gift);
        END IF;
      END LOOP;
 
      /* A line break by verse. */
      ADD(CHR(13));
    END LOOP;
 
    /* Return the song's lyrics. */
    RETURN lv_retval;
  END;
/

The typical test case for the function in PL/SQL is:

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/* Test the function in PL/SQL. */
SET SERVEROUTPUT ON SIZE UNLIMITED
DECLARE
  /*
  * Declare an lv_days array of an 8 character variable length string
  * and initialize it with values.
  */
  lv_days days := days('first','second','third','fourth'
                      ,'fifth','sixth','seventh','eighth'
                      ,'nineth','tenth','eleventh','twelfth');
 
  /*
  * Declare an lv_gifts array of the user-defined LYRIC data type and
  * initialize it with values.
  */
  lv_gifts lyrics := lyrics(lyric(DAY => 'and a', gift => 'Partridge in a pear tree')
                           ,lyric(DAY => 'Two', gift => 'Turtle doves')
                           ,lyric(DAY => 'Three', gift => 'French hens')
                           ,lyric(DAY => 'Four', gift => 'Calling birds')
                           ,lyric(DAY => 'Five', gift => 'Golden rings' )
                           ,lyric(DAY => 'Six', gift => 'Geese a laying')
                           ,lyric(DAY => 'Seven', gift => 'Swans a swimming')
                           ,lyric(DAY => 'Eight', gift => 'Maids a milking')
                           ,lyric(DAY => 'Nine', gift => 'Ladies dancing')
                           ,lyric(DAY => 'Ten', gift => 'Lords a leaping')
                           ,lyric(DAY => 'Eleven',gift => 'Pipers piping')
                           ,lyric(DAY => 'Twelve',gift => 'Drummers drumming'));
 
  /*
  * Declare an lv_days array of an 36 character variable length string
  * and initialize it with values.
  */
  lv_song song := song();
 
BEGIN
  /* Call the twelve_days function and assign the results to the local
  * lv_song variable.
  */
  lv_song := twelve_days(lv_days,lv_gifts);
 
  /*
  * Read the lines from the local lv_song variable and print them.
  */
  FOR i IN 1..lv_song.LAST LOOP
    dbms_output.put_line(lv_song(i));
  END LOOP;
END;
/

It displays:

On the first day of Christmas
my true love sent to me:
- A Partridge in a pear tree
 
On the second day of Christmas
my true love sent to me:
- Two Turtle doves
- and a Partridge in a pear tree
 
On the third day of Christmas
my true love sent to me:
- Three French hens
- Two Turtle doves
- and a Partridge in a pear tree
 
...
 
On the twelfth day of Christmas
my true love sent to me:
- Twelve Drummers drumming
- Eleven Pipers piping
- Ten Lords a leaping
- Nine Ladies dancing
- Eight Maids a milking
- Seven Swans a swimming
- Six Geese a laying
- Five Golden rings
- Four Calling birds
- Three French hens
- Two Turtle doves
- and a Partridge in a pear tree

As always, I hope this helps those learning how to write PL/SQL and/or code.

Reviewing old files, I thought posting my tkprof.ksh would be helpful. So, here’s the script that assumes you’re using Oracle e-Business Suite (Demo database, hence the APPS/APPS connection); and if I get a chance this summer I’ll convert it to Bash shell.

#!/bin/ksh
# -------------------------------------------------------------------------
# Author:   Michael McLaughlin
# Name:     tkprof.ksh
 
# Purpose:  The program takes the following arguments:
#           1. A directory
#           2. A search string
#           3. A target directory
#           It assumes raw trace files have an extension of ".trc".
#           The output file name follows this pattern (because it is
#           possible for multiple tracefiles to be written during the
#           same minute).
# -------------------------------------------------------------------------
 
# Function to find minimum field delimiter.
function min
{
  # Find the whitespace that preceeds the file date.
  until [[ $(ls -al $i | cut -c$minv-$minv) == " " ]]; do
    let minv=minv+1
  done
}
 
# Function to find maximum field delimiter.
function max
{
  # Find the whitespace that succeeds the file date.
  until [[ $(ls -al $i | cut -c$maxv-$maxv) == " " ]]; do
    let maxv=maxv+1
  done
}
 
# Debugging enabled by unremarking the "set -x"
# set -x
 
# Print header information
print =================================================================
print Running [tkprof.ksh] script ...
 
# Evaluate whether an argument is provide and if no argument
# is provided, then substitute the present working directory.
if   [[ $# == 0 ]]; then
  dir=${PWD}  
  str="*"
  des=${PWD}  
elif [[ $# == 1 ]]; then
  dir=${1}
  str="*"
  des=${1}
elif [[ $# == 2 ]]; then
  dir=${1}
  str=${2}
  des=${1}
elif [[ $# == 3 ]]; then
  dir=${1}
  str=${2}
  des=${3}
fi
 
# Evaluate whether the argument is a directory file.
if [[ -d ${dir} ]] && [[ -d ${des} ]]; then
 
  # Print what directory and search string are targets.
  print =================================================================
  print Run in tkprof from [${dir}] directory ...
  print The files contain a string of [${str}] ...
  print =================================================================
 
  # Evaluate whether the argument is the present working
  # directory and if not change directory to that target
  # directory so file type evaluation will work.
  if [[ ${dir} != ${PWD} ]]; then
    cd ${dir} 
  fi
 
  # Set file counter.
  let fcnt=0
 
  # Submit compression to the background as a job.
  for i in $(grep -li "${str}" *.trc); do
 
    # Evaluate whether file is an ordinary file.
    if [[ -f ${i} ]]; then
 
      # Set default values each iteration.
      let minv=40
      let maxv=53
 
      # Increment counter.
      let fcnt=fcnt+1
 
      # Call functions to reset min and max values where necessary.
      min ${i}
      max ${i}
 
      # Parse date stamp from trace file without multiple IO calls.
      # Assumption that the file is from the current year.
      date=$(ls -al ${i} | cut -c${minv}-${maxv}) 
      mon=$(echo ${date} | cut -c1-3)
      yr=$(date          | cut -c25-28)
 
      # Validate month is 10 or greater to pad for reduced whitespace.
      if (( $(echo ${date} | cut -c5-6) < 10 )); then
        day=0$(echo ${date}| cut -c5-5)
        hr=$(echo ${date}  | cut -c7-8)
        min=$(echo ${date} | cut -c10-11)
      else
        day=$(echo ${date} | cut -c5-6)
        hr=$(echo ${date}  | cut -c8-9)
        min=$(echo ${date} | cut -c11-12)
      fi
 
      fn=file${fcnt}_${day}-${mon}-${yr}_${hr}:${min}:${day}
 
      print Old [$i] and new [$des/$fn]
      tkprof ${i} ${des}/${fn}.prf explain=APPS/APPS sort='(prsela,exeela,fchela)'
 
      # Print what directory and search string are targets.
      print =================================================================
    fi
  done
 
else
  # Print message that a directory argument was not provided.
  print You failed to provie a single valid directory argument.
fi

I hope this helps those looking for a solution.

Every now and then, I get questions from folks about how to tune in-memory elements of their PL/SQL programs. This blog post address one of those core issues that some PL/SQL programmers avoid.

Specifically, it addresses how to convert a list of values into a structure (in C/C++ its a struct, in Java its an ArrayList, and PL/SQL it’s a table of scalar or object types). Oracle lingo hides the similarity by calling either an Attribute Definition Type (ADT) or User-Defined Type (UDT). The difference in the Oracle space is that an ADT deals with a type defined in DBMS_STANDARD package, which is more or less like a primitive type in Java.

Oracle does this for two reasons:

• They handle lists of standard types in a difference C++ class than they do UDT types.
• They rigidly adhere to Interface Definition Language (IDL) principles.

The cast_strings function converts a list of strings into a record data structure. It lets the list of strings have either a densely or sparsely populated list of values, and it calls the verify_date function to identify a DATE data type and regular expressions to identify numbers and strings.

You need to build a UDT object type and lists of both ADT and UDT data types.

/* Create a table of strings. */
CREATE OR REPLACE
  TYPE tre AS TABLE OF VARCHAR2(20);
/
 
/* Create a structure of a date, number, and string. */
CREATE OR REPLACE
  TYPE struct IS OBJECT
  ( xdate     DATE
  , xnumber  NUMBER
  , xstring  VARCHAR2(20));
/
 
/* Create a table of tre type. */
CREATE OR REPLACE
  TYPE structs IS TABLE OF struct;
/

The cast_strings function is defined below:

CREATE OR REPLACE
  FUNCTION cast_strings
  ( pv_list  TRE ) RETURN struct IS
 
  /* Declare a UDT and initialize an empty struct variable. */
  lv_retval  STRUCT := struct( xdate => NULL
                             , xnumber => NULL
					         , xstring => NULL); 
  BEGIN  
    /* Loop through list of values to find only the numbers. */
    FOR i IN 1..pv_list.LAST LOOP
      /* Ensure that a sparsely populated list can't fail. */
      IF pv_list.EXISTS(i) THEN
        /* Order if number evaluation before string evaluation. */
        CASE
          WHEN lv_retval.xnumber IS NULL AND REGEXP_LIKE(pv_list(i),'^[[:digit:]]*$') THEN
            lv_retval.xnumber := pv_list(i);
          WHEN verify_date(pv_list(i)) THEN
            IF lv_retval.xdate IS NULL THEN
              lv_retval.xdate := pv_list(i);
            ELSE
              lv_retval.xdate := NULL;
            END IF;
          WHEN lv_retval.xstring IS NULL AND REGEXP_LIKE(pv_list(i),'^[[:alnum:]]*$') THEN
            lv_retval.xstring := pv_list(i);
          ELSE
            NULL;
        END CASE;
      END IF;
    END LOOP;
 
    /* Print the results. */
    RETURN lv_retval;
  END;
/

There are three test cases for this function:

• The first use-case checks whether the input parameter is a sparsely or densely populated list:

  DECLARE /* Declare an input variable of three or more elements. */ lv_list TRE := tre('Berlin','25','09-May-1945','45');   /* Declare a variable to hold the compound type values. */ lv_struct STRUCT; BEGIN /* Make the set sparsely populated. */ lv_list.DELETE(2);   /* Test the cast_strings function. */ lv_struct := cast_strings(lv_list);   /* Print the values of the compound variable. */ dbms_output.put_line(CHR(10)); dbms_output.put_line('xstring ['||lv_struct.xstring||']'); dbms_output.put_line('xdate ['||TO_CHAR(lv_struct.xdate,'DD-MON-YYYY')||']'); dbms_output.put_line('xnumber ['||lv_struct.xnumber||']'); END; /

  DECLARE /* Declare an input variable of three or more elements. */ lv_list TRE := tre('Berlin','25','09-May-1945','45'); /* Declare a variable to hold the compound type values. */ lv_struct STRUCT; BEGIN /* Make the set sparsely populated. */ lv_list.DELETE(2); /* Test the cast_strings function. */ lv_struct := cast_strings(lv_list); /* Print the values of the compound variable. */ dbms_output.put_line(CHR(10)); dbms_output.put_line('xstring ['||lv_struct.xstring||']'); dbms_output.put_line('xdate ['||TO_CHAR(lv_struct.xdate,'DD-MON-YYYY')||']'); dbms_output.put_line('xnumber ['||lv_struct.xnumber||']'); END; /

  It should return:

  xstring [Berlin] xdate [09-MAY-1945] xnumber [45]

  xstring [Berlin] xdate [09-MAY-1945] xnumber [45]

  The program defines two numbers and deletes the first number, which is why it prints the second number.

• The second use-case checks with a list of only one element:

  SELECT TO_CHAR(xdate,'DD-MON-YYYY') AS xdate , xnumber , xstring FROM TABLE(structs(cast_strings(tre('catch22','25','25-Nov-1945'))));

  SELECT TO_CHAR(xdate,'DD-MON-YYYY') AS xdate , xnumber , xstring FROM TABLE(structs(cast_strings(tre('catch22','25','25-Nov-1945'))));

  It should return:

  XDATE XNUMBER XSTRING -------------------- ---------- -------------------- 25-NOV-1945 25 catch22

  XDATE XNUMBER XSTRING -------------------- ---------- -------------------- 25-NOV-1945 25 catch22

  The program returns a structure with values converted into their appropriate data type.

• The third use-case checks with a list of two elements:

  SELECT TO_CHAR(xdate,'DD-MON-YYYY') AS xdate , xnumber , xstring FROM TABLE(structs(cast_strings(tre('catch22','25','25-Nov-1945')) ,cast_strings(tre('31-APR-2017','1918','areodromes'))));

  SELECT TO_CHAR(xdate,'DD-MON-YYYY') AS xdate , xnumber , xstring FROM TABLE(structs(cast_strings(tre('catch22','25','25-Nov-1945')) ,cast_strings(tre('31-APR-2017','1918','areodromes'))));

  It should return:

  XDATE XNUMBER XSTRING -------------------- ---------- -------------------- 25-NOV-1945 25 catch22 1918 areodromes

  XDATE XNUMBER XSTRING -------------------- ---------- -------------------- 25-NOV-1945 25 catch22 1918 areodromes

  The program defines calls the cast_strings with a valid set of values and an invalid set of values. The invalid set of values contains a bad date in the set of values.

As always, I hope this helps those looking for how to solve this type of problem.

I was working on some test cases for my students and changing the behavior of a verify_date function that I wrote years ago to validate and returns valid dates when they’re passed as strings. The original program returned today’s date when the date was invalid.

The new function returns a BOOLEAN value of false by default and true when the string validates as a date. Unfortunately, I introduced a mistake that didn’t use to exist in Oracle 11g, which was the version when I wrote the original function.

The test cases in Oracle 21c raises the following error when an invalid date is passed to the CASE statement by the cast_strings function that calls the new verify_date function:

FROM   TABLE(structs(cast_strings(tre('31-APR-2017','1917','dirk'))))
                     *
ERROR AT line 2:
ORA-06592: CASE NOT found WHILE executing CASE statement
ORA-06512: AT "C##STUDENT.VERIFY_DATE", line 30
ORA-06512: AT "C##STUDENT.CAST_STRINGS", line 18

As you can see, the test case uses ’31-APR-2017′ as an incorrect date to verify the use-case. The error occurred because the ELSE clause in the CASE statement wasn’t provided. Previously, the ELSE clause was optional and setting the lv_retval return variable to FALSE in the DECLARE block made it unnecessary.

The fixed code follows:

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CREATE OR REPLACE
  FUNCTION verify_date
  ( pv_date_in  VARCHAR2) RETURN BOOLEAN IS
 
  /* Local variable to ensure case-insensitive comparison. */
  lv_date_in  VARCHAR2(11);
 
  /* Local return variable. */
  lv_date  BOOLEAN := FALSE;
BEGIN
  /* Convert string input to uppercase month. */
  lv_date_in := UPPER(pv_date_in);
 
  /* Check for a DD-MON-RR or DD-MON-YYYY string. */
  IF REGEXP_LIKE(lv_date_in,'^[0-9]{2,2}-[ADFJMNOS][ACEOPU][BCGLNPRTVY]-([0-9]{2,2}|[0-9]{4,4})$') THEN
    /* Case statement checks for 28 or 29, 30, or 31 day month. */
    CASE
      /* Valid 31 day month date value. */
      WHEN SUBSTR(lv_date_in,4,3) IN ('JAN','MAR','MAY','JUL','AUG','OCT','DEC') AND
           TO_NUMBER(SUBSTR(pv_date_in,1,2)) BETWEEN 1 AND 31 THEN 
        lv_date := TRUE;
      /* Valid 30 day month date value. */
      WHEN SUBSTR(lv_date_in,4,3) IN ('APR','JUN','SEP','NOV') AND
           TO_NUMBER(SUBSTR(pv_date_in,1,2)) BETWEEN 1 AND 30 THEN 
        lv_date := TRUE;
      /* Valid 28 or 29 day month date value. */
      WHEN SUBSTR(lv_date_in,4,3) = 'FEB' THEN
        /* Verify 2-digit or 4-digit year. */
        IF (LENGTH(pv_date_in) = 9 AND MOD(TO_NUMBER(SUBSTR(pv_date_in,8,2)) + 2000,4) = 0 OR
            LENGTH(pv_date_in) = 11 AND MOD(TO_NUMBER(SUBSTR(pv_date_in,8,4)),4) = 0) AND
            TO_NUMBER(SUBSTR(pv_date_in,1,2)) BETWEEN 1 AND 29 THEN
          lv_date := TRUE;
        ELSE /* Not a leap year. */
          IF TO_NUMBER(SUBSTR(pv_date_in,1,2)) BETWEEN 1 AND 28 THEN
            lv_date := TRUE;
          END IF;
        END IF;
      ELSE
        NULL;
    END CASE;
  END IF;
  /* Return date. */
  RETURN lv_date;
EXCEPTION
  WHEN VALUE_ERROR THEN
    RETURN lv_date;
END;
/

The new ELSE clause in on lines 31 and 32, and the converted function works. I also added a local lv_date_in variable to hold an uppercase version of an input string to: ensure a case-insensitive comparison of the month value, and avoid a having to pass the input as an IN OUT mode parameter. Typically, I leave off exception handlers because mistyping or copying for newer programmers becomes easier, but in this case I added an exception handler for strings that are larger than 11-characters.

As always, I hope this helps those looking for a solution to a coding problem.

As I move forward with trying to build an easy to use framework for data analysts who use multiple database backends and work on Windows OS, here’s a complete script that lets you run any query stored in a file to return a CSV file. It makes the assumption that you opted to put the user ID and password in the Windows ODBC DSN, and only provides the ODBC DSN name to make the connection to the ODBC library and database.

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# A local function for verbose reporting.
function Get-Message ($param, $value = $null) {
  if (!($value)) {
    Write-Host "Evaluate swtich    [" $param "]" } 	  
  else {
    Write-Host "Evaluate parameter [" $param "] and [" $value "]" } 
}
 
# Read SQLStatement file and minimally parse it.
function Get-SQLStatement ($sqlStatement) {
  # Set localvariable for return string value.
  $statement = ""
 
  # Read a file line-by-line.
  foreach ($line in Get-Content $sqlStatement) {
    # Use regular expression to replace multiple whitespace.
    $line = $line -replace '\s+', ' '
 
    # Add a whitespace to avoid joining keywords from different lines;
    # and remove trailing semicolons which are unneeded.
    if (!($line.endswith(";"))) {
      $statement += $line + " " }
    else {
      $statement += $line.trimend(";") }
  }
  # Returned minimally parsed statement.
  return $statement
}
 
# Set default type of SQL statement value to a query.
$stmt = "select"
 
# Set a variable to hold a SQL statement from a file.
$query = ""
 
# Set default values for SQL input and output files.
$outFile = "output.csv"
$sqlFile = "query.sql"
 
# Set default path to: %USERPROFILE%\AppData\Local\Temp folder, but ir 
# the tilde (~) in lieu of the %USERPROFILE% environment variable value.
$path = "~\AppData\Local\Temp"
 
# Set a verbose switch.
$verbose = $false
 
# Wrap the Parameter call to avoid a type casting warning.
try {
  param (
    [Parameter(Mandatory)][hashtable]$args
  )
}
catch {}
 
# Check for switches and parameters with arguments.
for ($i = 0; $i -lt $args.count; $i += 1) {
  if (($args[$i].startswith("-")) -and ($args[$i + 1].startswith("-"))) {
    if ($args[$i] = "-v") {
      $verbose = $true }
      # Print to verbose console.
    if ($verbose) { Get-Message $args[$i] }}
  elseif ($args[$i].startswith("-")) {
    # Print to verbose console.
    if ($verbose) { Get-Message $args[$i] $args[$i + 1] }
 
    # Evaluate and take action on parameters and values.
    if ($args[$i] -eq "-o") {
      $outfile = $args[$i + 1] }
    elseif ($args[$i] -eq "-q") {
      $sqlFile = $args[$i + 1] }
    elseif ($args[$i] -eq "-p") {
      $path = $args[$i + 1] }
  }
}
 
# Set a PowerShell Virtual Drive.
New-PSDrive -Name folder -PSProvider FileSystem -Description 'Forder Location' `
            -Root $path | Out-Null
 
# Remove the file only when it exists.
if (Test-Path folder:$outFile) {
  Remove-Item -Path folder:$outFile }
 
# Read SQL file into minimally parsed string.
if (Test-Path folder:$sqlFile) {
  $query = Get-SQLStatement $sqlFile }
 
# Set a ODBC DSN connection string.
$ConnectionString = 'DSN=OracleGeneric'
 
# Set an Oracle Command Object for a query.
$Connection = New-Object System.Data.Odbc.OdbcConnection;
$Connection.ConnectionString = $ConnectionString
 
# Attempt connection.
try {
  $Connection.Open()
 
  # Create a SQL command.
  $Command = $Connection.CreateCommand();
  $Command.CommandText = $query;
 
  # Attempt to read SQL command.
  try {
    $row = $Command.ExecuteReader();
 
    # Read while records are found.
    while ($row.Read()) {
      # Initialize output for each row.
      $output = ""
 
      # Navigate across all columns (only two in this example).
      for ($column = 0; $column -lt $row.FieldCount; $column += 1) {
        # Mechanic for comma-delimit between last and first name.  
        if ($output.length -eq 0) { 
          $output += $row[$column] }
        else {
          $output += ", " + $row[$column] }
      }
      # Write the output from the database to a file.
      Add-Content -Value $output -Path folder:$outFile
    }
  } catch {
    Write-Error "Message: $($_.Exception.Message)"
    Write-Error "StackTrace: $($_.Exception.StackTrace)"
    Write-Error "LoaderExceptions: $($_.Exception.LoaderExceptions)"
  } finally {
    # Close the reader.
    $row.Close() }
} catch {
  Write-Error "Message: $($_.Exception.Message)"
  Write-Error "StackTrace: $($_.Exception.StackTrace)"
  Write-Error "LoaderExceptions: $($_.Exception.LoaderExceptions)"
} finally {
  $Connection.Close() }

You can use a command-line call like this:

powershell ./OracleContact.ps1 -v -o output.csv -q script.sql -p .

It produces the following verbose output to the console:

Evaluate swtich    [ -v ]
Evaluate parameter [ -o ] and [ output.csv ]
Evaluate parameter [ -q ] and [ script.sql ]
Evaluate parameter [ -p ] and [ . ]

You can suppress printing to the console by eliminating the -v switch from the parameter list.

As always, I hope this helps those looking for a solution to less tedious interactions with the Oracle database.

Transaction Management

Learning Outcomes

• Learn how to use Multiversion Concurrency Control (MVCC).
• Learn how to manage ACID-compliant transactions.
• Learn how to use:
  • SAVEPOINT Statement
  • COMMIT Statement
  • ROLLBACK Statement

Lesson Material

Transaction Management involves two key components. One is Multiversion Concurrency Control (MVCC) so one user doesn’t interfere with another user. The other is data transactions. Data transactions packag SQL statements in the scope of an imperative language that uses Transaction Control Language (TCL) to extend ACID-compliance from single SQL statements to groups of SQL statements.

Multiversion Concurrency Control (MVCC)

Multiversion Concurrency Control (MVCC) uses database snapshots to provide transactions with memory-persistent copies of the database. This means that users, via their SQL statements, interact with the in-memory copies of data rather than directly with physical data. MVCC systems isolate user transactions from each other and guarantee transaction integrity by preventing dirty transactions, writes to the data that shouldn’t happen and that make the data inconsistent. Oracle Database 12c prevents dirty writes by its MVCC and transaction model.

Transaction models depend on transactions, which are ACID-compliant blocks of code. Oracle Database 12c provides an MVCC architecture that guarantees that all changes to data are ACID-compliant, which ensures the integrity of concurrent operations on data—transactions.

ACID-compliant transactions meet four conditions:

Atomic

They complete or fail while undoing any partial changes.

Consistent

They change from one state to another the same way regardless of whether
the change is made through parallel actions or serial actions.

Isolated

Partial changes are never seen by other users or processes in the concurrent system.

Durable

They are written to disk and made permanent when completed.

Oracle Database 12c manages ACID-compliant transactions by writing them to disk first, as redo log files only or as both redo log files and archive log files. Then it writes them to the database. This multiple-step process with logs ensures that Oracle database’s buffer cache (part of the instance memory) isn’t lost from any completed transaction. Log writes occur before the acknowledgement-of-transactions process occurs.

The smallest transaction in a database is a single SQL statement that inserts, updates, or deletes rows. SQL statements can also change values in one or more columns of a row in a table. Each SQL statement is by itself an ACID-compliant and MVCC-enabled transaction when managed by a transaction-capable database engine. The Oracle database is always a transaction-capable system. Transactions are typically a collection of SQL statements that work in close cooperation to accomplish a business objective. They’re often grouped into stored programs, which are functions, procedures, or triggers. Triggers are specialized programs that audit or protect data. They enforce business rules that prevent unauthorized changes to the data.

SQL statements and stored programs are foundational elements for development of business applications. They contain the interaction points between customers and the data and are collectively called the application programming interface (API) to the database. User forms (typically web forms today) access the API to interact with the data. In well-architected business application software, the API is the only interface that the form developer interacts with.

Database developers, such as you and I, create these code components to enforce business rules while providing options to form developers. In doing so, database developers must guard a few things at all cost. For example, some critical business logic and controls must prevent changes to the data in specific tables, even changes in API programs. That type of critical control is often written in database triggers. SQL statements are events that add, modify, or delete data. Triggers guarantee that API code cannot make certain additions, modifications, or deletions to critical resources, such as tables. Triggers can run before or after SQL statements. Their actions, like the SQL statements themselves, are temporary until the calling scope sends an instruction to commit the work performed.

A database trigger can intercept values before they’re placed in a column, and it can ensure that only certain values can be inserted into or updated in a column. A trigger overrides an INSERT or UPDATE statement value that violates a business rule and then it either raises an error and aborts the transaction or changes the value before it can be inserted or updated into the table. Chapter 12 offers examples of both types of triggers in Oracle Database 12c.
MVCC determines how to manage transactions. MVCC guarantees how multiple users’ SQL statements interact in an ACID compliant manner. The next two sections qualify how data transactions work and how MVCC locks and isolates partial results from data transactions.

Data Transaction

Data Manipulation Language (DML) commands are the SQL statements that transact against the data. They are principally the INSERT, UPDATE, and DELETE statements. The INSERT statement adds new rows in a table, the UPDATE statement modifies columns in existing rows, and the DELETE statement removes a row from a table.

The Oracle MERGE statement transacts against data by providing a conditional insert or update feature. The MERGE statement lets you add new rows when they don’t exist or change column values in rows that do exist.

Inserting data seldom encounters a conflict with other SQL statements because the values become a new row or rows in a table. Updates and deletes, on the other hand, can and do encounter conflicts with other UPDATE and DELETE statements. INSERT statements that encounter conflicts occur when columns in a new row match a preexisting row’s uniquely constrained columns. The insertion is disallowed because only one row can contain the unique column set.

These individual transactions have two phases in transactional databases such as Oracle. The first phase involves making a change that is visible only to the user in the current session. The user then has the option of committing the change, which makes it permanent, or rolling back the change, which undoes the transaction. Developers use Transaction Control Language (TCL) commands to confirm or cancel transactions. The COMMIT statement confirms or makes permanent any change, and the ROLLBACK statement cancels or undoes any change.

A generic transaction lifecycle for a two-table insert process implements a business rule that specifies that neither INSERT statement works unless they both work. Moreover, if the first INSERT statement fails, the second INSERT statement never runs; and if the second INSERT statement fails, the first INSERT statement is undone by a ROLLBACK statement to a SAVEPOINT.

After a failed transaction is unwritten, good development practice requires that you write the failed event(s) to an error log table. The write succeeds because it occurs after the ROLLBACK statement but before the COMMIT statement.

A SQL statement followed by a COMMIT statement is called a transaction process, or a two-phase commit (2PC) protocol. ACID-compliant transactions use a 2PC protocol to manage one SQL statement or collections of SQL statements. In a 2PC protocol model, the INSERT, UPDATE, MERGE, or DELETE DML statement starts the process and submits changes. These DML statements can also act as events that fire database triggers assigned to the table being changed.

Transactions become more complex when they include database triggers because triggers can inject an entire layer of logic within the transaction scope of a DML statement. For example, database triggers can do the following:

• Run code that verifies, changes, or repudiates submitted changes
• Record additional information after validation in other tables (they can’t write to the table being changed—or, in database lexicon, “mutated”
• Throw exceptions to terminate a transaction when the values don’t meet business rules

As a general rule, triggers can’t contain a COMMIT or ROLLBACK statement because they run inside the transaction scope of a DML statement. Oracle databases give developers an alternative to this general rule because they support autonomous transactions. Autonomous transactions run outside the transaction scope of the triggering DML statement. They can contain a COMMIT statement and act independently of the calling scope statement. This means an autonomous trigger can commit a transaction when the calling transaction fails.

As independent statements or collections of statements add, modify, and remove rows, one statement transacts against data only by locking rows: the SELECT statement. A SELECT statement typically doesn’t lock rows when it acts as a cursor in the scope of a stored program. A cursor is a data structure that contains rows of one-to-many columns in a stored program. This is also known as a list of record structures.

Cursors act like ordinary SQL queries, except they’re managed by procedure programs row by row. There are many examples of procedural programming languages. PL/SQL and SQL/PSM programming languages are procedural languages designed to run inside the database. C, C++, C#, Java, Perl, and PHP are procedural languages that interface with the database through well-defined interfaces, such as Java Database Connectivity (JDBC) and Open Database Connectivity (ODBC).

Cursors can query data two ways. One way locks the rows so that they can’t be changed until the cursor is closed; closing the cursor releases the lock. The other way doesn’t lock the rows, which allows them to be changed while the program is working with the data set from the cursor. The safest practice is to lock the rows when you open the cursor, and that should always be the case when you’re inserting, updating, or deleting rows that depend on the values in the cursor not changing until the transaction lifecycle of the program unit completes.

Loops use cursors to process data sets. That means the cursors are generally opened at or near the beginning of program units. Inside the loop the values from the cursor support one to many SQL statements for one to many tables.

Stored and external programs create their operational scope inside a database connection when they’re called by another program. External programs connect to a database and enjoy their own operational scope, known as a session scope. The session defines the programs’ operational scope. The operational scope of a stored program or external program defines the transaction scope. Inside the transaction scope, the programs interact with data in tables by inserting, updating, or deleting data until the operations complete successfully or encounter a critical failure. These stored program units commit changes when everything completes successfully, or they roll back changes when any critical instruction fails. Sometimes, the programs are written to roll back changes when any instruction fails.

In the Oracle Database, the most common clause to lock rows is the FOR UPDATE clause, which is appended to a SELECT statement. An Oracle database also supports a WAIT n seconds or NOWAIT option. The WAIT option is a blessing when you want to reply to an end user form’s request and can’t make the change quickly. Without this option, a change could hang around for a long time, which means virtually indefinitely to a user trying to run your application. The default value in an Oracle database is NOWAIT, WAIT without a timeout, or wait indefinitely.

You should avoid this default behavior when developing program units that interact with customers. The Oracle Database also supports a full table lock with the SQL LOCK TABLE command, but you would need to embed the command inside a stored or external program’s instruction set.

A unit test script may contain SQL or PL/SQL statements or it may call another script file that contains SQL or PL/SQL statements. Moreover, a script file is a way to bundle several activities into a single file because most unit test programs typically run two or more instructions as unit tests.

Unconditional Script File

You can write a simple unit test like the example program provided in the Lab 1 Help Section, which includes conditional logic. However, you can write a simpler script that is unconditional and raises exceptions when preconditions do not exist.

The following script file creates a one table and one_s sequence. The DROP TABLE and DROP SEQUENCE statements have the same precondition, which is that the table or sequence must previously exist.

-- Drop table one.
DROP TABLE one;
 
-- Crete table one.
CREATE TABLE one
( one_id    NUMBER
, one_text  VARCHAR2(10));
 
-- Drop sequence one_s.
DROP SEQUENCE one_s;
 
-- Create sequence one_s.
CREATE SEQUENCE one_s;

After writing the script file, you can save it in the lab2 subdirectory as the unconditional.sql file. After you login to the SQL*Plus environment from the lab2 subdirectory. You call the unconditional.sql script file from inside the SQL*Plus environment with the following syntax:

@unconditional.sql

It will display the following output, which raises an exception when the one table or one_s sequence does not already exist in the schema or database:

DROP TABLE one
           *
ERROR at line 1:
ORA-00942: table or view does not exist
 
Table created.
 
DROP SEQUENCE one_s
              *
ERROR at line 1:
ORA-02289: sequence does not exist
 
Sequence created.

An unconditional script raises exceptions when a precondition of the statement does not exist. The precondition is not limited to objects, like the table or sequence; and the precondition may be specific data in one or several rows of one or several tables. You can avoid raising conditional errors by writing conditional scripts.

Conditional Script File

A conditional script file contains statements that check for a precondition before running a statement, which effectively promotes their embedded statements to a lambda function. The following logic recreates the logic of the unconditional.sql script file as a conditional script file:

-- Conditionally drop a table and sequence.
BEGIN
  FOR i IN (SELECT   object_name
            ,        object_type
            FROM     user_objects
            WHERE    object_name IN ('ONE','ONE_S')
            ORDER BY object_type ) LOOP
    IF i.object_type = 'TABLE' THEN
      EXECUTE IMMEDIATE 'DROP TABLE '||i.object_name||' CASCADE CONSTRAINTS';
    ELSE
      EXECUTE IMMEDIATE 'DROP SEQUENCE '||i.object_name;
    END IF;
  END LOOP;
END;
/
 
-- Crete table one.
CREATE TABLE one
( one_id    NUMBER
, one_text  VARCHAR2(10));
 
-- Create sequence one_s.
CREATE SEQUENCE one_s;

You can save this script in the lab2 subdirectory as conditional.sql and then unit test it in SQL*Plus. You must manually drop the one table and one_s sequence before running the conditional.sql script to test the preconditions.

You will see that the conditional.sql script does not raise an exception because the one table or one_s sequence is missing. It should generate output to the console, like this:

PL/SQL procedure successfully completed.
 
Table created.
 
Sequence created.

As a rule, you should always write conditional script files. Unconditional script files throw meaningless errors, which may cause your good code to fail a deployment test that requires error free code.

Selective Aggregation

Learning Outcomes

• Learn how to combine CASE operators and aggregation functions.
• Learn how to selective aggregate values.
• Learn how to use SQL to format report output.

Selective aggregation is the combination of the CASE operator and aggregation functions. Any aggregation function adds, sums, or averages the numbers that it finds; and when you embed the results of a CASE operator inside an aggregation function you get a selective result. The selectivity is determined by the WHEN clause of a CASE operator, which is more or less like an IF statement in an imperative programming language.

The prototype for selective aggregation is illustrated with a SUM function below:

SELECT   SUM(CASE
               WHEN left_operand = right_operand THEN result
               WHEN left_operand > right_operand THEN result
               WHEN left_operand IN (SET OF comma-delimited VALUES) THEN result
               WHEN left_operand IN (query OF results) THEN result
               ELSE alt_result
             END) AS selective_aggregate
FROM     some_table;

A small example let’s you see how selective aggregation works. You create a PAYMENT table and PAYMENT_S sequence for this example, as follows:

-- Create a PAYMENT table.
CREATE TABLE payment
( payment_id     NUMBER
, payment_date   DATE	      CONSTRAINT nn_payment_1 NOT NULL
, payment_amount NUMBER(20,2) CONSTRAINT nn_payment_2 NOT NULL
, CONSTRAINT pk_payment PRIMARY KEY (payment_id));
 
-- Create a PAYMENT_S sequence.
CREATE SEQUENCE payment_s;

After you create the table and sequence, you should insert some data. You can match the values below or choose your own values. You should just insert values for a bunch of rows.

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DECLARE
  -- Create local collection data types.
  TYPE pmtval IS TABLE OF NUMBER(20,2);
  TYPE smonth IS TABLE OF VARCHAR2(3);
 
  -- Create variable to hold the list of payments.
  payments PMTVAL := pmtval();
 
  -- Declare month arrays.
  short_month SMONTH := smonth('JAN','FEB','MAR','APR','MAY','JUN'
                              ,'JUL','AUG','SEP','OCT','NOV','DEC');
 
  -- Declare variable values.
  month      VARCHAR2(3);
  year       NUMBER := '2019';
  pmt_date   DATE; 
  tpmt_date  VARCHAR2(11);
 
  -- Declare default number of random payments.
  payment_number  NUMBER := 10000;
BEGIN
  -- Populate payment list. 
  FOR i IN 1..payment_number LOOP
    payments.EXTEND;
    SELECT   ROUND(dbms_random.value() * 1000,0)
    ||       '.'
    ||       ROUND(dbms_random.value() * 100,0)
    INTO     payments(payments.COUNT)
    FROM     dual;
  END LOOP;
 
  -- Create and populate payment date and amount.
  FOR i IN 1..payment_number LOOP
    -- Assign random month value.
    month := short_month(dbms_random.value(1,short_month.COUNT));
 
    -- Assign random day of the month value and assemble random date.
    IF month IN ('JAN','MAR','MAY','JUL','AUG','OCT','DEC') THEN
      pmt_date := ROUND(dbms_random.value(1,31),0) || '-' || month || '-' || year;
    ELSIF month IN ('APR','JUN','SEP','NOV') THEN
      pmt_date := ROUND(dbms_random.value(1,30),0) || '-' || month || '-' || year;
    ELSE
      pmt_date := ROUND(dbms_random.value(1,28),0) || '-' || month || '-' || year;
    END IF;
 
    -- Insert values into the PAYMENT table.
    INSERT INTO payment
    ( payment_id, payment_date, payment_amount )
    VALUES
    ( payment_s.NEXTVAL, pmt_date, payments(i));
  END LOOP;
 
  -- Commit the writes.
  COMMIT;
END;
/

After inserting 10,000 rows, you can get an unformatted total with the following query:

-- Query total amount.
SELECT   SUM(payment_amount) AS payment_total
FROM     payment;

It outputs the following:

PAYMENT_TOTAL
-------------
   5011091.75

You can nest the result inside the TO_CHAR function to format the output, like

-- Query total formatted amount.
SELECT   TO_CHAR(SUM(payment_amount),'999,999,999.00') AS payment_total
FROM     payment;

It outputs the following:

PAYMENT_TOTAL
---------------
   5,011,091.75

Somebody may suggest that you use a PIVOT function to rotate the data into a summary by month but the PIVOT function has limits. The pivoting key must be numeric and the column values will use only those numeric values.

-- Pivoted summaries by numeric monthly value.
SELECT   *
FROM    (SELECT EXTRACT(MONTH FROM payment_date) payment_month
         ,      payment_amount
         FROM   payment)
         PIVOT (SUM(payment_amount) FOR payment_month IN
                 (1,2,3,4,5,6,7,8,9,10,11,12));

It outputs the following:

	 1	    2	       3	  4	     5		6	   7	      8 	 9	   10	      11	 12
---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------
 245896.55  430552.36  443742.63  457860.27  470467.18	466370.71  415158.28  439898.72  458998.09  461378.56  474499.22  246269.18

You can use selective aggregation to get the results by a character label, like

SELECT   SUM(
           CASE
             WHEN EXTRACT(MONTH FROM payment_date) = 1
             AND  EXTRACT(YEAR FROM payment_date) = 2019  THEN payment_amount
           END) AS "JAN"
,        SUM(
           CASE
             WHEN EXTRACT(MONTH FROM payment_date) = 2
             AND  EXTRACT(YEAR FROM payment_date) = 2019  THEN payment_amount
           END) AS "FEB"
,        SUM(
           CASE
             WHEN EXTRACT(MONTH FROM payment_date) = 3
             AND  EXTRACT(YEAR FROM payment_date) = 2019  THEN payment_amount
           END) AS "MAR"
,        SUM(
           CASE
             WHEN EXTRACT(MONTH FROM payment_date) IN (1,2,3)
             AND  EXTRACT(YEAR FROM payment_date) = 2019 THEN payment_amount
           END) AS "1FQ"
,        SUM(
           CASE
             WHEN EXTRACT(MONTH FROM payment_date) = 4
             AND  EXTRACT(YEAR FROM payment_date) = 2019  THEN payment_amount
           END) AS "APR"
FROM     payment;

It outputs the following:

       JAN	  FEB	     MAR	1FQ	   APR
---------- ---------- ---------- ---------- ----------
 245896.55  430552.36  443742.63 1120191.54  457860.27

You can format the output with a combination of the TO_CHAR and LPAD functions. The TO_CHAR allows you to add a formatting mask, complete with commas and two mandatory digits to the right of the decimal point. The reformatted query looks like

COL JAN FORMAT A13 HEADING "Jan"
COL FEB FORMAT A13 HEADING "Feb"
COL MAR FORMAT A13 HEADING "Mar"
COL 1FQ FORMAT A13 HEADING "1FQ"
COL APR FORMAT A13 HEADING "Apr"
SELECT   LPAD(TO_CHAR(SUM(
           CASE
             WHEN EXTRACT(MONTH FROM payment_date) = 1
             AND  EXTRACT(YEAR FROM payment_date) = 2019  THEN payment_amount
           END),'9,999,999.00'),13,' ') AS "JAN"
,        LPAD(TO_CHAR(SUM(
           CASE
             WHEN EXTRACT(MONTH FROM payment_date) = 2
             AND  EXTRACT(YEAR FROM payment_date) = 2019  THEN payment_amount
           END),'9,999,999.00'),13,' ') AS "FEB"
,        LPAD(TO_CHAR(SUM(
           CASE
             WHEN EXTRACT(MONTH FROM payment_date) = 3
             AND  EXTRACT(YEAR FROM payment_date) = 2019  THEN payment_amount
           END),'9,999,999.00'),13,' ') AS "MAR"
,        LPAD(TO_CHAR(SUM(
           CASE
             WHEN EXTRACT(MONTH FROM payment_date) IN (1,2,3)
             AND  EXTRACT(YEAR FROM payment_date) = 2019 THEN payment_amount
           END),'9,999,999.00'),13,' ') AS "1FQ"
,        LPAD(TO_CHAR(SUM(
           CASE
             WHEN EXTRACT(MONTH FROM payment_date) = 4
             AND  EXTRACT(YEAR FROM payment_date) = 2019  THEN payment_amount
           END),'9,999,999.00'),13,' ') AS "APR"
FROM     payment;

It displays the formatted output:

Jan	      Feb	    Mar 	  1FQ		Apr
------------- ------------- ------------- ------------- -------------
   245,896.55	 430,552.36    443,742.63  1,120,191.54    457,860.27

INSERT Statement

Learning Outcomes

• Learn how to use positional- and named-notation in INSERT statements.
• Learn how to use the VALUES clause in INSERT statements.
• Learn how to use subqueries in INSERT statements.

The INSERT statement lets you enter data into tables and views in two ways: via an INSERT statement with a VALUES clause and via an INSERT statement with a query. The VALUES clause takes a list of literal values (strings, numbers, and dates represented as strings), expression values (return values from functions), or variable values.

Query values are results from SELECT statements that are subqueries (covered earlier in this appendix). INSERT statements work with scalar, single-row, and multiple-row subqueries. The list of columns in the VALUES clause or SELECT clause of a query (a SELECT list) must map to the positional list of columns that defines the table. That list is found in the data dictionary or catalog. Alternatively to the list of columns from the data catalog, you can provide a named list of those columns. The named list overrides the positional (or default) order from the data catalog and must provide at least all mandatory columns in the table definition. Mandatory columns are those that are not null constrained.

Oracle databases differ from other databases in how they implement the INSERT statement. Oracle doesn’t support multiple-row inserts with a VALUES clause. Oracle does support default and override signatures as qualified in the ANSI SQL standards. Oracle also provides a multiple- table INSERT statement. This section covers how you enter data with an INSERT statement that is based on a VALUES clause or a subquery result statement. It also covers multiple-table INSERT statements.

The INSERT statement has one significant limitation: its default signature. The default signature is the list of columns that defines the table in the data catalog. The list is defined by the position and data type of columns. The CREATE statement defines the initial default signature, and the ALTER statement can change the number, data types, or ordering of columns in the default signature.

The default prototype for an INSERT statement allows for an optional column list that overrides the default list of columns. When you provide the column list you choose to implement named-notation, which is the right way to do it. Relying on the insertion order of the columns is a bad idea. An INSERT statement without a list of column names is a position-notation statement. Position-notation is bad because somebody can alter that order and previously written INSERT statements will break or put data in the wrong columns.

Like methods in OOPLs, an INSERT statement without the optional column list constructs an instance (or row) of the table using the default constructor. The override constructor for a row is defined by any INSERT statement when you provide an optional column list. That’s because it overrides the default constructor.

The generic prototype for an INSERT statement is confusing when it tries to capture both the VALUES clause and the result set from a query. Therefore, I’ve opted to provide two generic prototypes.

Insert by value

The first uses the VALUES clause:

INSERT
INTO table_name
[( column1, column2, column3, ...)] VALUES
( value1, value2, value3, ...);

Notice that the prototype for an INSERT statement with the result set from a query doesn’t use the VALUES clause at all. A parsing error occurs when the VALUES clause and query both occur in an INSERT statement.

The second prototype uses a query and excludes the VALUES clause. The subquery may return one to many rows of data. The operative rule is that all columns in the query return the same number of rows of data, because query results should be rectangles—rectangles made up of one to many rows of columns.

Insert by subquery

Here’s the prototype for an INSERT statement that uses a subquery:

INSERT
INTO table_name
[( column1, column2, column3, ...)]
( SELECT value1, value2, value3, ... FROM table_name WHERE ...);

A query, or SELECT statement, returns a SELECT list. The SELECT list is the list of columns, and it’s evaluated by position and data type. The SELECT list must match the definition of the table or the override signature provided.

Default signatures present a risk of data corruption through insertion anomalies, which occur when you enter bad data in tables. Mistakes transposing or misplacing values can occur more frequently with a default signature, because the underlying table structure can change. As a best practice, always use named notation by providing the optional list of values; this should help you avoid putting the right data in the wrong place.

The following subsections provide examples that use the default and override syntax for INSERT statements in Oracle databases. The subsections also cover multiple-table INSERT statements and a RETURNING INTO clause, which is an extension of the ANSI SQL standard. Oracle uses the RETURNING INTO clause to manage large objects, to return autogenerated identity column values, and to support some of the features of Oracle’s dynamic SQL. Note that Oracle also supports a bulk INSERT statement, which requires knowledge of PL/SQL.

DESCRIBE table_name

Name                                 Null?    Type
------------------------------------ -------- --------
RENTAL_ID                            NOT NULL NUMBER
CUSTOMER_ID                          NOT NULL NUMBER
CHECK_OUT_DATE                       NOT NULL DATE
RETURN_DATE                                   DATE
CREATED_BY                           NOT NULL NUMBER
CREATION_DATE                        NOT NULL DATE
LAST_UPDATED_BY                      NOT NULL NUMBER
LAST_UPDATE_DATE                     NOT NULL DATE

Name                                      Null?    Type
------------------------------------ -------- --------
RENTAL_ID                            NOT NULL NUMBER
CUSTOMER_ID                          NOT NULL NUMBER
CHECK_OUT_DATE                       NOT NULL DATE
RETURN_DATE                                   DATE
CREATED_BY                           NOT NULL NUMBER
CREATION_DATE                        NOT NULL DATE
LAST_UPDATED_BY                      NOT NULL NUMBER
LAST_UPDATE_DATE                     NOT NULL DATE

SQL> INSERT INTO rental
  2  VALUES
  3  ( 1086
  4  , 1009
  5  , SYSDATE
  6  , TRUNC(SYSDATE + 5) 7 ,1
  8  , SYSDATE
  9  , 1
 10  , SYSDATE);

  5  , TO_DATE('15-APR-2011 12:53:01','DD-MON-YYYY HH24:MI:SS')

  5  , CAST('15-APR-2011 12:53:02' AS DATE)

  5  ,  CAST('15-APR-2011 12:53:02' AS DATE) FROM dual
        *
ERROR AT line 1:
ORA-01830: DATE format picture ends before converting entire input string

  5  ,  CAST(CAST('15-APR-2011 12:53:02' AS TIMESTAMP) AS DATE)

SQL> SELECT   rental_s1.NEXTVAL FROM dual;

  3  ( rental_s1.NEXTVAL

SQL> SELECT   contact_id
  2  FROM     contact
  3  WHERE    last_name = 'Potter'
  4  AND      first_name = 'Harry';

SQL> INSERT INTO rental
  2  ( rental_id
  3  , customer_id
  4  , check_out_date
  5  , return_date
  6  , created_by
  7  , creation_date
  8  , last_updated_by
  9  , last_update_date )
10 VALUES
 11  ( rental_s1.NEXTVAL
 12  ,(SELECT   contact_id
 13    FROM     contact
 14    WHERE    last_name = 'Potter'
 15    AND      first_name = 'Harry')
 16  , SYSDATE
 17  , TRUNC(SYSDATE + 5)
 18  , 1
 19  , SYSDATE
 20  , 3
 21  , SYSDATE);

,(SELECT   contact_id
  *
ERROR AT line 3:
ORA-01427: single-ROW subquery returns more than one ROW

Name                             Null?    Type
 ------------------------------- -------- -----------------------
ITEM_DESC                        NOT NULL CLOB
ITEM_ICON                        NOT NULL BLOB
ITEM_PHOTO                                BINARY FILE LOB

EMPTY_BLOB()
EMPTY_CLOB()

 10  , BFILENAME('VIRTUAL_DIRECTORY_NAME', 'file_name.png')

INSERT INTO some_table
[( column1, column2, column3, ...)]
VALUES
( value1, value2, value3, ...)
RETURNING column1 INTO local_variable;

Name                                 Null?    Type
------------------------------------ -------- --------------
PARENT_ID                            NOT NULL NUMBER
PARENT_NAME                                   VARCHAR2(10)

Name                                 Null?    Type
------------------------------------ -------- --------------
CHILD_ID                             NOT NULL NUMBER
PARENT_ID                                     NUMBER
PARENT_NAME                                   VARCHAR2(10)

SQL> INSERT INTO parent
  2  VALUES
  3  ( parent_s1.NEXTVAL 4 ,'One Parent');
 
SQL> INSERT INTO child
  2  VALUES
  3  ( child_s1.NEXTVAL 4 , parent_s1.CURRVAL 5 ,'One Child');

SQL> INSERT INTO child
  2  VALUES
  3  ( child_s1.NEXTVAL -- CHILD_ID
  4  , parent_s1.CURRVAL -- PARENT_ID
  5  ,'One Child') -- CHILD_NAME
  6  /

INSERT
INTO table_name
[( column1, column2, column3, ...)]
( SELECT value1, value2, value3, ... FROM table_name WHERE ...);