# MacLochlainns Weblog

Michael McLaughlin's Technical Blog

## Functions disallow NDS

My students asked if you could embed an OFFSET x ROWS FETCH NEXT y ROWS ONLY clause in a SQL Server T-SQL user-defined function. The answer is no, it isn’t Oracle (yes, you can do that in Oracle Database 12c with an NDS statement). There’s an example in Chapter 2 of my Oracle Database 12c PL/SQL Programming book if you’re interested. I also demonstrate a different approach to SQL Server T-SQL table functions in this older post. However, an attempt to add the clause to a SQL Server T-SQL function, like this:

CREATE FUNCTION studentdb.getBatch (@rows AS INT ,@offset AS INT) RETURNS @output TABLE ( marvel_id INT , avenger_name VARCHAR(30) , first_name VARCHAR(20) , last_name VARCHAR(20)) AS BEGIN /* Insert the results into the table variable. */ INSERT @output SELECT marvel_id , avenger_name , first_name , last_name FROM studentdb.marvel OFFSET (@offset - 1) ROWS FETCH NEXT @rows ROWS ONLY;   /* Return the table variable from the function. */ RETURN; END;

Throws the following errors trying to compile the function:

Msg 102, Level 15, State 1, Procedure getBatch, Line 16 Incorrect syntax near '@offset'. Msg 153, Level 15, State 2, Procedure getBatch, Line 16 Invalid usage of the option NEXT in the FETCH statement.

If you have a strong background in Oracle and can sort through the dynamic SQL syntax for T-SQL, you might try re-writing the function to use the EXEC SP_EXECUTESQL @var; command. That rewrite that attempts to use NDS (Native Dynamic SQL) would look like this:

CREATE FUNCTION studentdb.getBatch (@rows AS INT ,@offset AS INT) RETURNS @output TABLE ( marvel_id INT , avenger_name VARCHAR(30) , first_name VARCHAR(20) , last_name VARCHAR(20)) AS BEGIN DECLARE /* Declare a variable for a dynamic SQL statement. */ @stmt VARCHAR(400);   /* Assign the SQL statement to a variable. */ SET @stmt = N'SELECT marvel_id ' + N', avenger_name ' + N', first_name ' + N', last_name ' + N'FROM studentdb.marvel ' + N'OFFSET ' + (@offset - 1) + N' ' + N'ROWS FETCH NEXT ' + @rows + N' ROWS ONLY;'; BEGIN /* Insert the results into the table variable. */ INSERT @output EXEC sp_executesql @stmt; END;   /* Return the table variable from the function. */ RETURN; END;

Throws the following exception because you can’t use dynamic dispatch inside a T-SQL function:

Msg 443, Level 16, State 14, Procedure getBatch, Line 23 Invalid use of a side-effecting operator 'INSERT EXEC' within a function.

On the other hand you can rewrite the statement with a BETWEEN operator and it works somewhat like an OFFSET and FETCH operation. That refactored function would be written as follows:

CREATE FUNCTION studentdb.getBatch (@rowa AS INT ,@rowb AS INT) RETURNS @output TABLE ( marvel_id INT , avenger_name VARCHAR(30) , first_name VARCHAR(20) , last_name VARCHAR(20)) AS BEGIN /* Insert the results into the table variable. */ INSERT @output SELECT marvel_id , avenger_name , first_name , last_name FROM studentdb.marvel WHERE marvel_id BETWEEN @rowa AND @rowb;   /* Return the table variable from the function. */ RETURN; END;

It doesn’t raise an exception. You can call the table function like this:

SELECT * FROM getBatch(2,3);

It returns the two rows for Iron Man and Black Widow. As always, I hope this helps.

If you want to create the test case, here’s the script you need:

SELECT 'Conditionally drop studentdb.marvel table.' AS "Statement"; IF OBJECT_ID('studentdb.marvel','U') IS NOT NULL DROP TABLE studentdb.marvel;   SELECT 'Create studentdb.marvel table.' AS "Statement"; CREATE TABLE studentdb.marvel ( marvel_id INT NOT NULL IDENTITY(1,1) CONSTRAINT marvel_pk PRIMARY KEY , avenger_name VARCHAR(30) NOT NULL , first_name VARCHAR(20) NOT NULL , last_name VARCHAR(20) NOT NULL);   /* Insert the rows. */ INSERT INTO studentdb.marvel (avenger_name, first_name, last_name) VALUES ('Hulk','Bruce','Banner'); INSERT INTO studentdb.marvel (avenger_name, first_name, last_name) VALUES ('Iron Man','Tony','Stark'); INSERT INTO studentdb.marvel (avenger_name, first_name, last_name) VALUES ('Black Widow','Natasha','Romanoff'); INSERT INTO studentdb.marvel (avenger_name, first_name, last_name) VALUES ('Thor','Thor','Odinsson'); INSERT INTO studentdb.marvel (avenger_name, first_name, last_name) VALUES ('Captain America','Steve','Rogers'); INSERT INTO studentdb.marvel (avenger_name, first_name, last_name) VALUES ('Hawkeye','Clint','Barton'); INSERT INTO studentdb.marvel (avenger_name, first_name, last_name) VALUES ('Winter Soldier','Bucky','Barnes'); INSERT INTO studentdb.marvel (avenger_name, first_name, last_name) VALUES ('Iron Patriot','James','Rhodey');   /* Query the contents of the MARVEL table. */ SELECT * FROM studentdb.marvel;

Written by maclochlainn

February 14th, 2015 at 5:20 pm

## Filtering String Dates

A question came up about how to verify dates from a string without throwing a casting error because of a non-conforming date. You can throw a number of exceptions, and I wrote a function to filter bad string formats like the DD-MON-RR or DD-MON-YYYY.

The first one is for a day between 1 and the last day of month, which is:

ORA-01847: day of month must be between 1 and last day of month

An incorrect string for a month, raises the following error:

ORA-01843: not a valid month

A date format mask longer than a DD-MON-RR or DD-MON-YYYY raises the following exception:

ORA-01830: date format picture ends before converting entire input string

The verify_date function checks for non-conforming DD-MON-RR and DD-MON-YYYY date masks, and substitutes a SYSDATE value for a bad date entry:

CREATE OR REPLACE FUNCTION verify_date ( pv_date_in VARCHAR2) RETURN DATE IS /* Local return variable. */ lv_date DATE; BEGIN /* Check for a DD-MON-RR or DD-MON-YYYY string. */ IF REGEXP_LIKE(pv_date_in,'^[0-9]{2,}-[ADFJMNOS][ACEOPU][BCGLNPRTVY]-([0-9]{2,}|[0-9]{4,})$') THEN /* Case statement checks for 28 or 29, 30, or 31 day month. */ CASE /* Valid 31 day month date value. */ WHEN SUBSTR(pv_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 := pv_date_in; /* Valid 30 day month date value. */ WHEN SUBSTR(pv_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 := pv_date_in; /* Valid 28 or 29 day month date value. */ WHEN SUBSTR(pv_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 := pv_date_in; ELSE /* Not a leap year. */ IF TO_NUMBER(SUBSTR(pv_date_in,1,2)) BETWEEN 1 AND 28 THEN lv_date := pv_date_in; ELSE lv_date := SYSDATE; END IF; END IF; ELSE /* Assign a default date. */ lv_date := SYSDATE; END CASE; ELSE /* Assign a default date. */ lv_date := SYSDATE; END IF; /* Return date. */ RETURN lv_date; END; / You can check valid dates with a DD-MON-RR format: SELECT verify_date('28-FEB-10') AS "Non-Leap Year" , verify_date('29-FEB-12') AS "Leap Year" , verify_date('31-MAR-14') AS "31-Day Year" , verify_date('30-APR-14') AS "30-Day Year" FROM dual; You can check valid dates with a DD-MON-YYYY format: SELECT verify_date('28-FEB-2010') AS "Non-Leap Year" , verify_date('29-FEB-2012') AS "Leap Year" , verify_date('31-MAR-2014') AS "31-Day Year" , verify_date('30-APR-2014') AS "30-Day Year" FROM dual; They both return: Non-Leap Leap YEAR 31-DAY YEAR 30-DAY YEAR ----------- --------- ----------- ----------- 28-FEB-10 29-FEB-12 31-MAR-14 30-APR-14 You can check badly formatted dates with the following query: SELECT verify_date('28-FEB-2010') AS "Non-Leap Year" , verify_date('29-FEB-2012') AS "Leap Year" , verify_date('31-MAR-2014') AS "31-Day Year" , verify_date('30-APR-2014') AS "30-Day Year" FROM dual; You can screen for an alphanumeric string with the following expression: SELECT 'Valid alphanumeric string literal' AS "Statement" FROM dual WHERE REGEXP_LIKE('Some Mythical String$200','([:alnum:]|[:punct:]|[:space:])*');

You can screen for a numeric literal as a string with the following expression:

SELECT 'Valid numeric literal' AS "Statement" FROM dual WHERE REGEXP_LIKE('123.00','([:digit:]|[:punct:])');

As always, I hope this helps those who need this type of solution.

Written by maclochlainn

February 2nd, 2015 at 12:53 am

## PL/SQL Fall Through?

Somebody wants to know how you can write a PL/SQL solution that mimics the fall through of a switch statement because PL/SQL doesn’t support a switch statement (it does support a simple and searched CASE statement without fall through). It’s a question that I found interesting because there wasn’t a need for it when I figured out what he wanted to accomplish. Essentially, he wanted to know how to implement a nested loop where the first loop runs in ascending order and the nested loop runs in descending order based on the value of the outer loop.

While it seems Christmas songs aren’t politically correct, The Twelve Days of Christmas lets me show you how to implement a coupled nested loop. The easiest way to implement a solution requires an object type, like

1 2 3 4 5 CREATE OR REPLACE TYPE lyric IS OBJECT ( day_name VARCHAR2(8) , gift_name VARCHAR2(24)); /

The following anonymous block program shows you how to couple the performance of nested loops to print the lyrics from two collections:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 DECLARE /* Declare an array of days and gifts. */ TYPE days IS TABLE OF VARCHAR2(8); TYPE gifts IS TABLE OF lyric;   /* Initialize the collection of days. */ lv_days DAYS := days( 'first', 'second', 'third', 'fourth' , 'fifth', 'sixth', 'seventh', 'eighth' , 'nineth', 'tenth', 'eleventh', 'twelfth');   /* Initialize the collection of lyrics. */ lv_gifts GIFTS := gifts( lyric('and a', 'Partridge in a Pear Tree') , lyric('Two', 'Turtle Doves') , lyric('Three', 'French Hens') , lyric('Four', 'Calling Birds') , lyric('Five', 'Golden Rings' ) , lyric('Six', 'Geese a Laying') , lyric('Seven', 'Swans a Swimming') , lyric('Eight', 'Maids a Milking') , lyric('Nine', 'Maids a Milking') , lyric('Ten', 'Lords a Leaping') , lyric('Eleven', 'Pipers Piping') , lyric('Twelve', 'Drummers Drumming')); BEGIN /* Read forward through the days. */ FOR i IN 1..lv_days.COUNT LOOP DBMS_OUTPUT.put_line('On the ' || lv_days(i) || ' day of Christmas'); DBMS_OUTPUT.put_line('my true love sent to me:');   /* Read backward through the lyrics based on the ascending value of the day. */ FOR j IN REVERSE 1..i LOOP IF i = 1 THEN DBMS_OUTPUT.put_line('-'||'A'||' '||lv_gifts(j).gift_name); ELSE DBMS_OUTPUT.put_line('-'||lv_gifts(j).day_name||' '||lv_gifts(j).gift_name); END IF; END LOOP;   /* A line break by verse. */ DBMS_OUTPUT.put_line(CHR(10)); END LOOP; END; /

The FOR loop on line 31 descends from the current index of the ascending out loop. This shows you how to couple the performance of outer and inner loops. It let’s you print The Twelve Days of Christmas, as:

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 fourth day of Christmas my true love sent to me: -Four Calling Birds -Three French Hens -Two Turtle Doves -and a Partridge in a Pear Tree     On the fifth day of Christmas my true love sent to me: -Five Golden Rings -Four Calling Birds -Three French Hens -Two Turtle Doves -and a Partridge in a Pear Tree     On the sixth day of Christmas my true love sent to me: -Six Geese a Laying -Five Golden Rings -Four Calling Birds -Three French Hens -Two Turtle Doves -and a Partridge in a Pear Tree     On the seventh day of Christmas my true love sent to me: -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     On the eighth day of Christmas my true love sent to me: -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     On the nineth day of Christmas my true love sent to me: -Nine Maids a Milking -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     On the tenth day of Christmas my true love sent to me: -Ten Lords a Leaping -Nine Maids a Milking -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     On the eleventh day of Christmas my true love sent to me: -Eleven Pipers Piping -Ten Lords a Leaping -Nine Maids a Milking -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     On the twelfth day of Christmas my true love sent to me: -Twelve Drummers Drumming -Eleven Pipers Piping -Ten Lords a Leaping -Nine Maids a Milking -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

My conclusion is that the PL/SQL language doesn’t need to support fall through because it provides a simpler and more effective solution with coupled nested loops. As always, I hope the example helps those interested in a solution.

Written by maclochlainn

January 18th, 2015 at 12:13 am

## Querying an Object Type

I demonstrated a number of SQL approaches to reading object types in Appendix B of the Oracle Database 12c PL/SQL Programming book. For example, the easiest one to construct and return the results from a TO_STRING member function uses the TREAT function:

SELECT TREAT(base_t() AS base_t).to_string() AS "Text" FROM dual;

However, it seems that I could have provided one more. Here’s an example of how you can test the construction of an object type and how you can return its attributes with a query. It’s important to note that there’s a natural problem with this syntax when you increment a sequence inside the object type. The problem is that it double increments the counter for the sequence.

SELECT * FROM TABLE(SELECT CAST(COLLECT(base_t()) AS base_t_tab) FROM dual);

The syntax for the COLLECT function requires that you put it inside a SELECT-list. Then, the CAST function converts a single instance of the BASE_T object type to a one element BASE_T_TAB collection. Finally, the TABLE function returns a single row from the BASE_T_TAB collection.

You can find a more complete article covering column substitutability and object types and subtypes on the ToadWorld site. I think it helps clear up how you can effectively write PL/SQL types and subtypes for persistent object type columns.

Written by maclochlainn

November 25th, 2014 at 12:33 am

## Finding Direct Indexes

If you’re not using Toad DBA Suite, it’s sometimes hard to find solutions. Somebody wanted to know how to find indexes that aren’t indirect. Indirect indexes are those created for a primary key because a primary key column or set of columns are both not null and uniquely constrained. Likewise, you create a unique index when you can create a unique constraint. You can’t drop a unique index for a primary key without dropping the primary key or unique constraint that indirectly created it.

The following query returns indexes with one or more columns that are created by a CREATE INDEX statement on a target table. It excludes unique indexes created by a primary key constraint, and it returns the relative position of columns in an index:

COLUMN sequence_name FORMAT A22 HEADING "Sequence Name" COLUMN column_position FORMAT 999 HEADING "Column|Position" COLUMN column_name FORMAT A22 HEADING "Column|Name" SELECT uin.index_name , uic.column_position , uic.column_name FROM user_indexes uin INNER JOIN user_ind_columns uic ON uin.index_name = uic.index_name AND uin.table_name = uic.table_name WHERE uin.table_name = UPPER('&&table_name') AND NOT uin.index_name IN (SELECT constraint_name FROM user_constraints WHERE table_name = UPPER('&&table_name')) ORDER BY uin.index_name , uic.column_position;

It can be rewritten into a function, which can then drop indexes based on a table name:

CREATE OR REPLACE FUNCTION drop_indexes_on ( pv_table_name VARCHAR2 ) RETURN NUMBER IS   /* A return value. */ lv_return NUMBER := 0;   /* A query to return only directly created indexes. */ CURSOR find_indexes_on ( cv_table_name VARCHAR2 ) IS SELECT DISTINCT ui.index_name FROM user_indexes ui INNER JOIN user_ind_columns uic ON ui.index_name = uic.index_name AND ui.table_name = uic.table_name WHERE ui.table_name = UPPER(cv_table_name) AND NOT ui.index_name IN (SELECT constraint_name FROM user_constraints WHERE table_name = UPPER(cv_table_name));   /* Declare function autonomous. */ PRAGMA AUTONOMOUS_TRANSACTION;   BEGIN   /* Drop the indexes on a table. */ FOR i IN find_indexes_on(pv_table_name) LOOP EXECUTE IMMEDIATE 'DROP INDEX '||i.index_name; lv_return := 1; END LOOP;   RETURN lv_return; END drop_indexes_on; /

You can call the drop_on_indexes_on function like this:

SELECT drop_indexes_on(UPPER('address_lab')) FROM dual;

Hope this helps those who need to work with dropping indexes.

Written by maclochlainn

November 23rd, 2014 at 8:42 pm

## Parsing DBMS_OUTPUT

Testing with DBMS_OUTPUT.PUT_LINE is always a bit of a problem when you have strings longer than 80 characters in length, which occurs more frequently with Oracle Database 12c. An example of managing output occurs when you want to print a string with embedded line breaks. My solution is the following parse_rows procedure:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 CREATE OR REPLACE PROCEDURE parse_rows ( pv_text VARCHAR2 ) IS   /* Declare parsing indexes. */ lv_start NUMBER := 1; lv_end NUMBER := 1; lv_length NUMBER;   BEGIN   /* Assign an end value based on parsing line return or length. */ IF INSTR(pv_text,CHR(10),lv_start) = 0 THEN lv_end := LENGTH(pv_text) + 1; ELSE lv_end := INSTR(pv_text,CHR(10),lv_start); END IF;   /* Assign a length value to the parsed string. */ lv_length := lv_end - lv_start;   /* Print first line. */ DBMS_OUTPUT.put_line(SUBSTR(pv_text,lv_start,lv_length));   /* Print the rows of a multiple line string. */ WHILE (lv_end < LENGTH(pv_text)) LOOP   /* Assign a new start value. */ lv_start := lv_end + 1;   /* Assign a new end value. */ IF INSTR(pv_text,CHR(10),lv_start + 1) = 0 THEN lv_end := LENGTH(pv_text) + 1; ELSE lv_end := INSTR(pv_text,CHR(10),lv_start + 1); END IF;   /* Assign a new length. */ lv_length := lv_end - lv_start;   /* Print the individual rows. */ DBMS_OUTPUT.put_line(SUBSTR(pv_text,lv_start,lv_length));   END LOOP; END; /

Here’s the example of a test program for the procedure:

1 2 3 4 5 6 7 DECLARE /* Declare text. */ lv_text VARCHAR2(200) := 'This is too much'||CHR(10)||'information'||CHR(10)||'on one line.'; BEGIN parse_rows(lv_text); END; /

It prints the following:

1 2 3 This is too much information on one line.

Hope this benefits those looking for quick solution.

Written by maclochlainn

May 21st, 2014 at 12:35 am

## Oracle 12c VARCHAR2?

The Oracle Database 12c documentation says you can set the maximum size of a VARCHAR2 to 32,767 bytes. That’s true except when you’re trying to map a large Java string to a VARCHAR2. It fails when the physical size of the Java string is greater than 4,000 bytes with an ORA-01002 or fetch out of sequence error.

SELECT read_text_file('C:\Data\loader\Hobbit1.txt') * ERROR at line 1: ORA-24345: A Truncation or null fetch error occurred   ERROR: ORA-01002: fetch out of sequence

You need to grant privileges before you can test this code. You can grant privileges by connecting as the SYS user of a CDB (or non-multitenant database) or as the ADMIN user of a PDB with the AS SYSDBA clause. Then, you run the following command to grant external file access to the JVM inside Oracle Database 12c:

BEGIN DBMS_JAVA.GRANT_PERMISSION('IMPORTER' ,'SYS:java.io.FilePermission' ,'C:\Data\Loader\Hobbit1.txt' ,'read'); END; /

The IMPORTER is a PDB user name, or a non-multitenant database user name. Please note that permissions must be granted on each physical file.

Here’s the code that raises the error when the external file is greater than 4,000 bytes:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 CREATE OR REPLACE AND COMPILE JAVA SOURCE NAMED "ReadFile" AS // Java library imports. import java.io.File; import java.io.BufferedReader; import java.io.FileNotFoundException; import java.io.IOException; import java.io.FileReader; import java.security.AccessControlException;   // Class definition. public class ReadFile { // Define class variables. private static File file; private static FileReader inTextFile; private static BufferedReader inTextReader; private static StringBuffer output = new StringBuffer(); private static String outLine, outText;   // Define readText() method. public static String readText(String fromFile) throws AccessControlException, IOException { // Read file. try { // Initialize File. file = new File(fromFile);   // Check for valid file. if (file.exists()) {   // Assign file to a stream. inTextFile = new FileReader(file); inTextReader = new BufferedReader(inTextFile);   // Read character-by-character. while ((outLine = inTextReader.readLine()) != null) { output.append(outLine + "\n"); }   // Assing the StringBuffer to a String. outText = output.toString();   // Close File. inTextFile.close(); } else { outText = new String("Empty"); }} catch (IOException e) { outText = new String(""); return outText; } return outText; }} /

The PL/SQL wrapper should look like this:

1 2 3 4 5 CREATE OR REPLACE FUNCTION read_text_file (from_file VARCHAR2) RETURN VARCHAR2 IS LANGUAGE JAVA NAME 'ReadFile.readText(java.lang.String) return java.lang.String'; /

Then, you can query it like so:

SELECT read_text_file('C:\Data\loader\Hobbit1.txt') FROM dual;

You can avoid the error by returning the Java file size as a CLOB data type with the following Java source code.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 CREATE OR REPLACE AND COMPILE JAVA SOURCE NAMED "ReadFile" AS // Java library imports. import java.io.File; import java.io.BufferedReader; import java.io.FileNotFoundException; import java.io.IOException; import java.io.FileReader; import java.security.AccessControlException; import java.sql.*; import oracle.sql.driver.*; import oracle.sql.*;   // Class definition. public class ReadFile { // Define class variables. private static int i; private static File file; private static FileReader inTextFile; private static BufferedReader inTextReader; private static StringBuffer output = new StringBuffer(); private static String outLine, outText; private static CLOB outCLOB;   // Define readText() method. public static oracle.sql.CLOB readText(String fromFile) throws AccessControlException, IOException, SQLException { // Read file. try { // Initialize File. file = new File(fromFile);   // Check for valid file. if (file.exists()) {   // Assign file to a stream. inTextFile = new FileReader(file); inTextReader = new BufferedReader(inTextFile);   // Read character-by-character. while ((outLine = inTextReader.readLine()) != null) { output.append(outLine + "\n"); }   // Assing the StringBuffer to a String. outText = output.toString();   // Declare an Oracle connection. Connection conn = DriverManager.getConnection("jdbc:default:connection:");   // Transfer the String to CLOB. outCLOB = CLOB.createTemporary((oracle.jdbc.OracleConnectionWrapper) conn, true, CLOB.DURATION_SESSION); i = outCLOB.setString(1,outText);   // Close File. inTextFile.close(); } else { i = outCLOB.setString(1,"Empty"); }} catch (IOException e) { i = outCLOB.setString(1,""); return outCLOB; } return outCLOB; }} /

The wrapper changes to return a CLOB and map a java.sql.CLOB as the return type of the Java library. This command works:

1 2 3 4 5 CREATE OR REPLACE FUNCTION read_clob_file (from_file VARCHAR2) RETURN CLOB IS LANGUAGE JAVA NAME 'ReadFile.readText(java.lang.String) return oracle.sql.CLOB'; /

You now query the PL/SQL wrapper with this type of effective SQL*Plus command-line command:

COLUMN atext FORMAT A60 HEADING "Text" COLUMN asize FORMAT 99,999 HEADING "Size"   SELECT read_clob_file('C:\Data\loader\Hobbit1.txt') AS AText , LENGTH(read_clob_file('C:\Data\loader\Hobbit1.txt')) AS ASize FROM dual;

As always, I hope this helps somebody.

Written by maclochlainn

May 7th, 2014 at 3:03 am

## Best UTL_FILE Practice

In a post a couple days ago, I promised to provide a best practice approach to reading external files with the UTL_FILE package. My first assumption is that you’re reading unstructured data because structured data is best read by external tables because external tables can read data much faster with the PARALLEL option.

My second assumption is that you’re you don’t know how to use or choose not to use the DBMS_LOB package; specifically, the loadclobfromfile and loadblobfromfile procedures. By the way, Chapter 10 of the Oracle Database 12c PL/SQL Programming has several complete examples using the DBMS_LOB package. My third assumption is that you’d like the external file packaged as a whole, which means you want it returned as a CLOB or BLOB data type.

Here’s a generic function that achieves that and avoids the nonsense with closing the file in the exception handler, or worse yet, wrapping it in another PL/SQL schema-level function:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 CREATE OR REPLACE FUNCTION read_file_to_clob ( pv_location VARCHAR2 , pv_file_name VARCHAR2 ) RETURN CLOB IS   /* Declare local input variables. */ lv_location VARCHAR2(60); lv_file_name VARCHAR2(40);   /* Declare a file reference pointer and buffer. */ lv_file UTL_FILE.FILE_TYPE; -- File reference lv_line VARCHAR2(32767); -- Reading buffer   /* Declare local sizing variables. */ lv_file_size NUMBER; lv_line_size NUMBER; lv_read_size NUMBER :=0;   /* Declare local file attribute data. */ lv_file_exists BOOLEAN := FALSE; lv_block_size BINARY_INTEGER;   /* Declare a control variable and return CLOB variable. */ lv_enable BOOLEAN := FALSE; lv_return CLOB; BEGIN /* Declare local input variables. */ lv_location := pv_location; lv_file_name := pv_file_name;   /* Check for open file and close when open. */ IF UTL_FILE.is_open(lv_file) THEN UTL_FILE.fclose(lv_file); END IF;   /* Read the file attributes to get the physical size. */ UTL_FILE.fgetattr( location => lv_location , filename => lv_file_name , fexists => lv_file_exists , file_length => lv_file_size , block_size => lv_block_size );   /* Open only files that exist. */ IF lv_file_exists THEN   /* Create a temporary CLOB in memory. */ DBMS_LOB.createtemporary(lv_return, FALSE, DBMS_LOB.CALL);   /* Open the file for read-only of 32,767 byte lines. */ lv_file := UTL_FILE.fopen( location => lv_location , filename => lv_file_name , open_mode => 'R' , max_linesize => 32767);     /* Read all lines of a text file. */ WHILE (lv_read_size < lv_file_size) LOOP /* Read a line of text until the eof marker. */ UTL_FILE.get_line( file => lv_file , buffer => lv_line );   /* Add the line terminator or 2 bytes to its length. */ lv_line := NVL(lv_line,'')||CHR(10); lv_read_size := lv_read_size + LENGTH(NVL(lv_line,CHR(10))) + 2;   /* Write to an empty CLOB or append to an existing CLOB. */ IF NOT lv_enable THEN /* Write to the temporary CLOB variable. */ DBMS_LOB.WRITE( lv_return, LENGTH(lv_line), 1, lv_line);   /* Set the control variable. */ lv_enable := TRUE; ELSE /* Append to the temporary CLOB variable. */ DBMS_LOB.writeappend( lv_return, LENGTH(lv_line),lv_line); END IF; END LOOP;   /* Close the file. */ UTL_FILE.fclose(lv_file); END IF;   /* This line is never reached. */ RETURN lv_return; EXCEPTION WHEN OTHERS THEN UTL_FILE.fclose(lv_file); RAISE NO_DATA_FOUND; END; /

You can test the function with the following:

SET LONG 100000 SET PAGESIZE 999   SELECT read_file_to_clob('SomeVirtualDirectory','TextFile.txt') AS "Output" FROM dual;

If anybody has suggestions for improvements, please pass them along. As always, I hope this helps other developers.

Written by maclochlainn

April 16th, 2014 at 3:07 am

## Using UTL_FILE Package

Sometimes I’m surprised. Today, the surprise came when somebody pointed to a potential error in another author’s book. The person who asked the question had to send me a screen shot before I believed it.

The author’s code encounters the following error because the code was designed to loop through a multiple line file, and the code called the UTL_FILE.FOPEN procedure with three instead of four parameters. While it works with only three parameters when the strings are less than or equal to 1,024 (thanks Gary), it throws read errors when a string exceeds the default. You use the fourth parameter when your string exceeds the default length of 1,024.

DECLARE * ERROR AT line 1: ORA-29284: FILE read error ORA-06512: AT "SYS.UTL_FILE", line 106 ORA-06512: AT "SYS.UTL_FILE", line 746 ORA-06512: AT line 26

As mentioned, you fix the problem by using the fourth parameter like the call on lines 15 through 18 below:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 DECLARE /* Declare local input variables. */ lv_location VARCHAR2(60) := 'C:\Data\Direct'; lv_file_name VARCHAR2(40) := 'TextFile.txt';   /* Declare a file reference pointer and buffer. */ lv_file UTL_FILE.FILE_TYPE; -- File reference lv_line VARCHAR2(32767); -- Reading buffer   BEGIN   /* Check for open file and close when open. */ IF UTL_FILE.is_open(lv_file) THEN UTL_FILE.fclose(lv_file); END IF;   /* Open the file for read-only of 32,767 lines of text. The fourth parameter is required when you want to use the GET_LINE procedure to read a file line-by-line. */ lv_file := UTL_FILE.fopen( location => lv_location , filename => lv_file_name , open_mode => 'R' , max_linesize => 32767);   /* Read all lines of a text file. */ LOOP /* Read a line of text, when the eof marker is found the get_line procedure raises a NO_DATA_FOUND error, which is why there's no explicit loop. */ UTL_FILE.get_line( file => lv_file , buffer => lv_line );   /* Print the line of text or a line return because UTL_FILE doesn't read line returns. */ DBMS_OUTPUT.put_line(NVL(lv_line,CHR(10)));   END LOOP;   EXCEPTION WHEN NO_DATA_FOUND THEN UTL_FILE.fclose(lv_file); END; /

While the foregoing is traditional and uses a physical directory path from the local server’s operating system, you can use a virtual directory from Oracle Database 10g forward. This physical directory is also defined in the utl_file_dir parameter of the database server. A virtual directory hides the physical directory from the application software, which simplifies physical file maintenance when you need to move the files.

3 lv_location VARCHAR2(60) := 'DirectVirtualDirectory';

The preceding example works, and I’ll put one out converting the external to CLOB later in the week.

Written by maclochlainn

April 13th, 2014 at 11:46 pm

## DBMS_JAVA Privilege Error?

It’s possible to get an error after granting privileges to an external file system. One of those errors is tedious to resolve until you understand the rules governing Java NIO file permissions.

You grant privileges to external file systems as the sys user with the grant_permission procedure of the dbms_java package, like

SQL> BEGIN 2 DBMS_JAVA.GRANT_PERMISSION('IMPORTER' 3 ,'SYS:java.io.FilePermission' 4 ,'C:\Data\Upload' 5 ,'read'); 6 END; 7 /

After you grant privileges to read, write, and delete files with Oracle’s dbms_java package, you must disconnect any active session to enjoy the new privileges. If you forget to disconnect and re-connect an active session, you get the following error message:

FROM TABLE(list_files(get_directory_path('STAGE'))) * ERROR AT line 2: ORA-29532: JAVA CALL terminated BY uncaught JAVA EXCEPTION: JAVA.security.AccessControlException: DIRECTORY permissions restricted.

The problem and fix are simple. The permissions aren’t in effect until after you disconnect and reconnect your active sessions. I put this there because when I Google’d it, there wasn’t an answer already.

While I’m on the topic of privilege errors, that aren’t really errors, I thought it would be helpful to qualify how the delete permission works because I couldn’t find it anywhere in the Oracle documentation (if somebody finds it let make a comment that enriches the discussion). Unlike the read and write permissions, the delete permission requires permissions on specific files.

If you only grant permission on like:

SQL> BEGIN 2 DBMS_JAVA.GRANT_PERMISSION('IMPORTER' 3 ,'SYS:java.io.FilePermission' 4 ,'C:\Data\Upload' 5 ,'read,write,delete'); 6 END; 7 /

You would get this message when trying to delete an external file:

BEGIN * ERROR AT line 1: ORA-29532: JAVA CALL terminated BY uncaught JAVA EXCEPTION: JAVA.security.AccessControlException: the Permission (JAVA.io.FilePermission c:\data\LOG\item_import.LOG read) has NOT been granted TO IMPORTER. The PL/SQL TO GRANT this IS dbms_java.grant_permission( 'IMPORTER', 'SYS:java.io.FilePermission', 'c:\data\log\item_import.log', 'read' ) ORA-06512: AT "IMPORTER.DELETE_FILE", line 1 ORA-06512: AT line 2

It requires that you grant permissions on individual files to have the privilege of deleting them from within Oracle. That grant would look like the following:

SQL> BEGIN 2 DBMS_JAVA.GRANT_PERMISSION('IMPORTER' 3 ,'SYS:java.io.FilePermission' 4 ,'C:\Data\Upload\item_import.log' 5 ,'read,write,delete'); 6 END; 7 /

As always, I hope this helps other developers.

Written by maclochlainn

March 29th, 2014 at 1:59 pm