Archive for the ‘pl/sql’ tag
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.
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.
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.
Hidden DBMS_JAVA Nuance
It always happens when I’m in a hurry. Yes, I ran into one of those pesky little features with Oracle’s DBMS_JAVA package. While I try to write entries with proper GeSHi case semantics, like everyone else I tend to write PL/SQL initially in lowercase. That led me to the discovery of this wonderful error message:
BEGIN * ERROR at line 1: ORA-29532: Java CALL TERMINATED BY uncaught Java exception: oracle.aurora.vm.IdNotFoundException: importer : USER OR ROLE id does NOT exist ORA-06512: at "SYS.DBMS_JAVA", line 705 ORA-06512: at line 2 |
The problem was simple, while not published, you must enter the user/schema name in uppercase text when calling DBMS_JAVA.GRANT_PERMISSION procedure. Here’s a proper example:
SQL> BEGIN 2 DBMS_JAVA.GRANT_PERMISSION('IMPORTER' 3 ,'SYS:java.io.FilePermission' 4 ,'C:\Data\Upload' 5 ,'read'); 6 END; 7 / |
If you change the IMPORTER string to lower or mixed case, you raise the aforementioned error. Quite an interesting tidbit that I missed from Oracle Database 10g until Oracle Database 12c. Hope this helps you avoid wondering what’s happening when your line 2 looks like this:
2 DBMS_JAVA.GRANT_PERMISSION('Importer' |
As always, I hope this helps others. If you like more on writing Java inside the Oracle database you can check this older post.
Speaking at UTOUG 2014
I’m off shortly to attend and speak at the Utah Oracle User Group’s Spring Training Days 2014, which is held at Salt Lake Community College – Larry H. Miller Campus. My presentation is on writing PL/SQL for Oracle Database 12c. We’ll be covering how you can best anchor PL/SQL cursors to include or exclude hidden columns, and how to work with identifying columns in the scope of multiple table inserts.
I have copy of Oracle Database 12c PL/SQL Programming to give away in my session and John Harper’s session. While the book is also available on Kindle, Mac OS X users can get it as a natively as an iBook on the Apple Store. I’ve got a copy on my iPad and it looks great. What I especially like is the search feature.
Find Type Dependents
Somebody thought it was nice to show how to drop object type dependents in Oracle Database 11g, but they thought I should show how you discover dependent object types first. More or less, they were concerned how they discover type dependents when they raise the following error:
DROP TYPE item_object * ERROR at line 1: ORA-02303: cannot DROP OR REPLACE a TYPE WITH TYPE OR TABLE dependents |
They had a great point, so here I’m providing and object table function (object table functions are covered in Chapter 8 of Oracle Database 12c PL/SQL Programming book) that displays an object dependency tree.
Unlike table functions in Microsoft SQL Server or PostgreSQL, Oracle requires that you create the object type before you can return a result set table from a parameter-driven function. Here’s the object type for this object table function:
1 2 3 4 5 6 7 8 9 10 11 | -- Create an object type that mimics a record structure. CREATE OR REPLACE TYPE type_tree IS object ( level_id NUMBER , type_name VARCHAR2(30) , object VARCHAR2(10) , parent_type VARCHAR2(30)); / -- Create a UDT Collection. CREATE OR REPLACE TYPE type_tree_table IS TABLE OF type_tree; / |
Now, you can create the object table function that returns an object type dependent tree. This function uses branching recursion because you need to walk the dependency tree. The cursor against the three types of metadata in the database catalog lets us walk the tree. Each object type, and their dependents may have:
- A dependent object type
- A dependent collection, which uses the object type as a base object type.
- A dependent schema function, which uses the object type as a parameter data type or return data type.
- A dependent schema procedure, which uses the object type as a parameter data type.
- A dependent package, which contains a function or procedure using the object type as a parameter data type, or a function using the object type as a return data type.
Here’s the type_dependent function that walks the tree and displays the hierarchical results:
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 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 | CREATE OR REPLACE FUNCTION type_dependents ( pv_base_object_type VARCHAR2 , pv_level_id NUMBER DEFAULT 1 , pv_collection TYPE_TREE_TABLE DEFAULT NULL ) RETURN TYPE_TREE_TABLE IS /* Declare a return data type. */ lv_level_id NUMBER; /* Declare item type. */ lv_type_name VARCHAR2(30); lv_object_type VARCHAR2(30); lv_parent_type VARCHAR2(30); /* Declare a collection variable. */ lv_collection TYPE_TREE_TABLE := type_tree_table(); lv_incoming TYPE_TREE_TABLE := type_tree_table(); /* The first part of the cursor finds the dependent type names of complex object types, and the second part of the cursor finds the dependent collection types. Effectively the set operator finds two distinct branches because you may use any base type as an element of a complex object or of a collection. */ CURSOR base_type ( cv_level_id NUMBER , cv_base_type VARCHAR2 ) IS SELECT (cv_level_id) AS level_id , LPAD(' ', 2*(cv_level_id - 1)) || ut.type_name AS type_name , ut.typecode AS object_type , NULL AS parent_type FROM user_types ut WHERE ut.type_name = cv_base_type; CURSOR dependent_type ( cv_level_id NUMBER , cv_base_type VARCHAR2 ) IS SELECT cv_level_id AS level_id , LPAD(' ', 2*(cv_level_id - 1)) || uta.type_name AS type_name , ut.typecode AS object_type , ut.type_name AS parent_type FROM user_type_attrs uta INNER JOIN user_types ut ON uta.attr_type_name = ut.type_name WHERE ut.type_name = cv_base_type UNION ALL SELECT cv_level_id AS level_id , LPAD(' ', 2*(cv_level_id - 1)) || uct.type_name AS type_name , CASE WHEN uct.coll_type = 'TABLE' THEN uct.coll_type ELSE 'VARRAY' END AS object_type , ut.type_name AS parent_type FROM user_types ut INNER JOIN user_coll_types uct ON ut.type_name = uct.elem_type_name WHERE uct.elem_type_name = cv_base_type UNION ALL SELECT cv_level_id AS level_id , CASE WHEN package_name IS NULL THEN LPAD(' ', 2*(cv_level_id - 1)) || ua.object_name ELSE LPAD(' ', 2*(cv_level_id - 1)) || ua.package_name END AS type_name , CASE WHEN package_name IS NULL THEN uo.object_type ELSE 'PACKAGE' END AS object_type , ua.type_name AS parent_type FROM user_arguments ua LEFT JOIN user_objects uo ON ua.package_name = uo.object_name OR ua.object_name = uo.object_name WHERE type_name = cv_base_type ORDER BY object_type; BEGIN /* Set the call level indicator. */ lv_level_id := pv_level_id; /* Check if the collection holds values, which should occur in recursive calls. */ IF pv_collection IS NOT NULL THEN lv_collection := pv_collection; ELSE /* Open the base type and record level 1. */ OPEN base_type (lv_level_id, pv_base_object_type); FETCH base_type INTO lv_level_id , lv_type_name , lv_object_type , lv_parent_type; CLOSE base_type; /* Extend the collection. */ lv_collection.EXTEND; lv_collection(lv_collection.COUNT) := type_tree( lv_level_id , lv_type_name , lv_object_type , lv_parent_type ); /* Increment the type dependency level. */ lv_level_id := lv_level_id + 1; END IF; /* Loop through and return records. */ FOR i IN dependent_type(lv_level_id, pv_base_object_type) LOOP /* Extend the collection. */ lv_collection.EXTEND; lv_collection(lv_collection.COUNT) := type_tree( i.level_id , i.type_name , i.object_type , i.parent_type ); /* Recursively call down to dependent types. */ IF i.type_name <> i.parent_type THEN lv_collection := type_dependents(TRIM(i.type_name), (lv_level_id + 1), lv_collection); END IF; END LOOP; /* Return 0 for false. */ RETURN lv_collection; END; / |
You would query the function with the TABLE function, like this:
COLUMN level_id FORMAT 99999 HEADING "Level|ID #" COLUMN type_name FORMAT A30 HEADING "Type Name" COLUMN object FORMAT A10 HEADING "Object Type" COLUMN parent_type FORMAT A30 HEADING "Parent Type" SELECT * FROM TABLE(type_dependents('ITEM_OBJECT',1)); |
It displays the following results based on the sample types created by the original blog post:
Level
ID # Type Name Object Typ Parent Type
------ ------------------------------ ---------- ------------------------
1 ITEM_OBJECT OBJECT
2 GET_ITEM_OBJECT FUNCTION ITEM_OBJECT
2 IDENTIFIED_OBJECT OBJECT ITEM_OBJECT
2 ITEM_PACKAGE PACKAGE ITEM_OBJECT
2 ITEM_TABLE TABLE ITEM_OBJECT
3 ITEM_ASYNC_TABLE COLLECTION ITEM_TABLE
4 ITEM_LIST TABLE ITEM_ASYNC_TABLE
2 ITEM_VARRAY VARRAY ITEM_OBJECT
3 ITEM_ASYNC_VARRAY COLLECTION ITEM_VARRAY
4 ITEM_ARRAY VARRAY ITEM_ASYNC_VARRAY
10 rows selected. |
I hope this helps those working with Oracle Database 10g (de-supported), 11g, or 12c. As a note, you don’t need to drop type dependents in Oracle 12c because it supports type evolution. I cover type evolution in Appendix B of Oracle Database 12c PL/SQL Programming. As always, I hope this helps those trying to determine type dependents in an Oracle database.
Oracle 12c Offset & Rows
Oracle Database 12c provides a limit syntax in SQL for a query with the following clause:
[OFFSET n ROWS] FETCH FIRST m ROWS ONLY |
Unfortunately, it can’t be used dynamically like this in a stored function or procedure:
CURSOR dynamic_cursor ( cv_offset NUMBER , cv_rows NUMBER ) IS SELECT i.item_title FROM item i OFFSET cv_offset ROWS FETCH FIRST cv_rows ROWS ONLY; |
If you attempt it, you would raise the following error:
CREATE OR REPLACE FUNCTION dynamic_range * ERROR at line 1: ORA-03113: end-of-file ON communication channel Process ID: 4516 SESSION ID: 78 Serial NUMBER: 4467 |
The easy solution is to simply write it as a function returning an ADT (Attribute Data Type) collection like:
1 2 3 | CREATE OR REPLACE TYPE item_title_table AS TABLE OF VARCHAR2(60); / |
The following dynamic_range function returns a collection with a dynamic range bound to the limiting clause:
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 | CREATE OR REPLACE FUNCTION dynamic_range ( pv_offset NUMBER , pv_rows NUMBER ) RETURN item_title_table IS /* Declare a collection type. */ lv_item_title_table ITEM_TITLE_TABLE := item_title_table(); /* Local variable length string. */ lv_item_title VARCHAR2(60); /* Declare a local counter. */ lv_counter NUMBER := 1; /* Local NDS statement and cursor variables. */ lv_stmt VARCHAR2(2000); lv_cursor SYS_REFCURSOR; BEGIN /* Assigned a dynamic SQL statement to local variable. */ lv_stmt := 'SELECT i.item_title'||CHR(10) || 'FROM item i'||CHR(10) || 'OFFSET :bv_offset ROWS FETCH FIRST :bv_rows ROWS ONLY'; /* Open cursor for dynamic DNS statement. */ OPEN lv_cursor FOR lv_stmt USING pv_offset, pv_rows; LOOP /* Fetch element from cursor and assign to local variable. */ FETCH lv_cursor INTO lv_item_title; /* Exit when no more record found. */ EXIT WHEN lv_cursor%NOTFOUND; /* Extend space, assign a value, and increment counter. */ lv_item_title_table.EXTEND; lv_item_title_table(lv_counter) := lv_item_title; lv_counter := lv_counter + 1; END LOOP; /* Close cursor. */ CLOSE lv_cursor; /* Return collection. */ RETURN lv_item_title_table; END; / |
By using, the following query:
1 2 | SELECT COLUMN_VALUE AS item_title FROM TABLE(dynamic_range(2,5)); |
Hope this helps anybody who wants to make the limiting clause dynamic. You can find out how to embed it in PHP in Chapter 2 of the Oracle Database 12c PL/SQL Programming.
OUT Parameter Trick
Raja asked a question but unfortunately, I was buried in the final aspects of the write of the new Oracle Database 12c PL/SQL Programming book. He wanted to know how to pass an object type as an OUT-only mode parameter from a procedure.
That’s a great question, and it’s actually simple once you understand the difference between Oracle object types and other data types. Oracle object types must always be initiated before you use them, which means you must initialize any OUT-only mode parameters at the top of your execution section, like this:
1 2 3 4 5 6 7 8 9 10 11 12 | CREATE OR REPLACE PROCEDURE reset_troll ( pv_troll OUT TROLL_OBJECT ) IS /* Troll default name. */ lv_troll_name VARCHAR2(20) := 'Bert'; BEGIN /* Initialize the incoming parameter by allocating memory to it. */ pv_troll := troll_object(); /* Set the name to something other than the 'Tom' default value. */ pv_troll.set_troll(lv_troll_name); END reset_troll; / |
Line 7 shows you the trick, initialize the incoming parameter because there isn’t an incoming parameter for an OUT-only mode parameter. The calling parameter to an OUT-only mode parameter is only a reference where PL/SQL will copy the internal object reference. While the calling parameter has been initialized, the reference to the call parameter’s object is where the internal object will be copied. The local program must first ensure a new memory location for a new instance of the object type before it can act on or return an object instance to the external reference. More or less, the internal object is copied to the calling object instance’s memory location when the procedure completes its execution.
Here’s the source code for the troll_object object type and body:
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 | CREATE OR REPLACE TYPE troll_object IS OBJECT ( troll VARCHAR2(20) , CONSTRUCTOR FUNCTION troll_object RETURN SELF AS RESULT , CONSTRUCTOR FUNCTION troll_object ( troll VARCHAR2 ) RETURN SELF AS RESULT , MEMBER FUNCTION get_troll RETURN VARCHAR2 , MEMBER PROCEDURE set_troll (troll VARCHAR2) , MEMBER FUNCTION to_string RETURN VARCHAR2) INSTANTIABLE NOT FINAL; / CREATE OR REPLACE TYPE BODY troll_object IS /* Default no-argument constructor. */ CONSTRUCTOR FUNCTION troll_object RETURN SELF AS RESULT IS troll TROLL_OBJECT := troll_object('Tom'); BEGIN SELF := troll; RETURN; END troll_object; /* Single argument constructor. */ CONSTRUCTOR FUNCTION troll_object (troll VARCHAR2) RETURN SELF AS RESULT IS BEGIN SELF.troll := troll; RETURN; END troll_object; /* A getter function. */ MEMBER FUNCTION get_troll RETURN VARCHAR2 IS BEGIN RETURN SELF.troll; END get_troll; /* A setter procedure. */ MEMBER PROCEDURE set_troll (troll VARCHAR2) IS BEGIN SELF.troll := troll; END set_troll; /* A function that returns the formatted object type's contents. */ MEMBER FUNCTION to_string RETURN VARCHAR2 IS BEGIN RETURN 'Hello '||SELF.troll; END to_string; END; / |
You can test the reset_troll procedure with the following anonymous block:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | /* Enable printing from a PL/SQL block. */ SET SERVEROUTPUT ON SIZE UNLIMITED /* Anonymous testing block. */ DECLARE lv_troll TROLL_OBJECT := troll_object('Bill'); BEGIN dbms_output.put_line('--------------------'); /* Prints 'Hello William' */ dbms_output.put_line(lv_troll.to_string()); dbms_output.put_line('--------------------'); reset_troll(lv_troll); /* Prints 'Hello Bert' */ dbms_output.put_line(lv_troll.to_string()); dbms_output.put_line('--------------------'); END; / |
If you remark out line 7 from the reset_troll procedure, you’d raise the following exception by the call on line 10 because the local object hasn’t been instantiated (given life). It means there’s no memory location allocated for the instantiated (instance of an object type).
-------------------- Hello Bill -------------------- DECLARE * ERROR at line 1: ORA-30625: method dispatch ON NULL SELF argument IS disallowed ORA-06512: at "VIDEO.RESET_TROLL", line 10 ORA-06512: at line 8 |
Hope this helps those trying to solve the same problem.
DBMS_COMPARISON Missing?
The dbms_comparison package isn’t deployed when you provision a pluggable databases (PDBs) in Oracle 12c. It appears to be a simple omission. At least, it let me manually compiled the dbms_comparison package with this syntax:
@?/rdbms/admin/dbmscmp.sql @?/rdbms/admin/prvtcmp.plb |
However, when I ran the code against the PDB it failed. The same code worked against a container database (CDB). It struck me as odd. The error stack wasn’t too useful, as you can see below:
1 2 3 4 5 6 7 8 9 10 | BEGIN * ERROR at line 1: ORA-06564: object "SYS"."COMPARE_NAME" does NOT exist ORA-06512: at "SYS.DBMS_LOGREP_UTIL", line 569 ORA-06512: at "SYS.DBMS_LOGREP_UTIL", line 602 ORA-06512: at "SYS.DBMS_CMP_INT", line 394 ORA-01403: no DATA found ORA-06512: at "SYS.DBMS_COMPARISON", line 764 ORA-06512: at line 2 |
My test was using two copies of a table with differences between column values. Both were deployed in the same CDB or PDB. That meant it was either a missing table or a problem with my database link. Here’s the statement that caused the failure:
7 8 9 10 11 12 | dbms_comparison.create_comparison(comparison_name => 'COMPARE_NAME' , schema_name => 'video' , object_name => 'MEMBER#1' , dblink_name => 'loopbackpdb' , remote_schema_name => 'video' , remote_object_name => 'MEMBER#2'); |
Unfortunately, there wasn’t any notable difference between the two database links. Playing around with it, I discovered the problem. While you don’t have to enclose your case sensitive password in double quotes for a CDB database link, you do need to enclose the password with double quotes in a PDB database link.
This database link fixed the problem:
1 2 3 | CREATE DATABASE LINK loopbackpdb CONNECT TO video IDENTIFIED BY "Video1" USING 'video'; |
The delimiting double quotes on line 2 fixed the problem. Hopefully, this helps somebody who runs into it too. Any way, according to this June 2013 Oracle White Paper it would appear as a bug because it’s an inconsistent behavior between a CDB and PDB.
Reset sequence START WITH
Two things contributed to this post. One was a student question about the difference between the MAX_VALUE of a sequence and the actual sequence value. The other was a comment on an earlier post addressing an NDS approach to resetting sequences.
The student wanted to understand why there were gaps in the sequence, since they created it with the default values, like this:
CREATE SEQUENCE sequence_name; |
A default sequence in an Oracle database sets the cache value to 20, which means you get gaps every time a new set is allocated. This Ask Tom question and answer holds that information.
The blog comment was on an NDS statement post. I wasn’t quite sure what the comment wanted because there really wasn’t a question or a complete code example. Having demonstrated how to dynamically drop and recreate a new sequence without a gap in a comment reply, I thought that was adequate.
Having pointed the student to the Ask Tom column and my answer, he wanted to know how to create a stored procedure to reset sequences dynamically. It took me a couple weeks to get back to this but here’s the procedure. The tricky element of the procedure is the “no binding values allowed” restriction placed on NDS statements that process DDL statements.
The procedure uses two local procedures and two local functinons. The local find_sequence finds a sequence name in the schema, and find_next_sequence function returns the next value. The local create_sequence and drop_sequence procedures respectively isolate the logic for dynamic drops and creates of the sequence.
Warning: The restriction with this design assumes that the table name and sequence name are linked by using the table name and an _ID suffix.
-- Declare an autonomous procedure to drop sequences. CREATE OR REPLACE PROCEDURE reset_sequence ( pv_table_name VARCHAR2 , pv_sequence_name VARCHAR2 , pv_cache_value NUMBER DEFAULT 0 ) IS -- Declares stubs to remove forward reference limits. PROCEDURE create_sequence ( pv_sequence_name VARCHAR2, pv_cache_value NUMBER ); PROCEDURE drop_sequence ( pv_sequence_name VARCHAR2 ); FUNCTION find_sequence ( pv_sequence_name VARCHAR2 ) RETURN VARCHAR2; FUNCTION find_next_sequence ( pv_table_name VARCHAR2 ) RETURN VARCHAR2; -- Drops sequence. PROCEDURE drop_sequence ( pv_sequence_name VARCHAR2 ) IS -- Declare local variable(s). lv_statement VARCHAR2(200); lv_sequence_name VARCHAR2(30); BEGIN /* Conditionally drop any sequence using a local function to find a valid sequence name before attempting to drop it. */ IF find_sequence(DBMS_ASSERT.SIMPLE_SQL_NAME(pv_sequence_name)) > 0 THEN /* Dynamically drop sequence, which requires concatenating the sanitized sequence name because you can't bind values on a DDL statement. */ lv_statement := 'DROP sequence '||DBMS_ASSERT.SIMPLE_SQL_NAME(pv_sequence_name); -- Execute statement immediately. EXECUTE IMMEDIATE lv_statement; END IF; END drop_sequence; -- Drops sequence. PROCEDURE create_sequence ( pv_sequence_name VARCHAR2 , pv_cache_value NUMBER ) IS -- Declare local variable(s). lv_statement VARCHAR2(200); lv_next_sequence NUMBER; BEGIN -- Assign the next sequence value if one exists. lv_next_sequence := find_next_sequence(pv_table_name); -- Check whether a cache value has been provided. IF pv_cache_value > 0 THEN /* Dynamically create a sequence statement with a new start value that is one greater than the highest value in the table that uses the sequence. */ lv_statement := 'CREATE SEQUENCE '||DBMS_ASSERT.SIMPLE_SQL_NAME(pv_sequence_name)||CHR(10) || 'MINVALUE 1 NOMAXVALUE INCREMENT BY 1'||CHR(10) || 'START WITH '||lv_next_sequence||' CACHE '||pv_cache_value||' NOORDER NOCYCLE'; ELSE /* Dynamically create a sequence statement with a new start value that is one greater than the highest value in the table that uses the sequence. */ lv_statement := 'CREATE SEQUENCE '||DBMS_ASSERT.SIMPLE_SQL_NAME(pv_sequence_name)||CHR(10) || ' MINVALUE 1 NOMAXVALUE'||CHR(10) || 'INCREMENT BY 1 START WITH '||lv_next_sequence||' NOCACHE NOORDER NOCYCLE'; END IF; -- Execute create sequence statement. EXECUTE IMMEDIATE lv_statement; END create_sequence; -- Finds whether a sequence exists. FUNCTION find_sequence ( pv_sequence_name VARCHAR2 ) RETURN VARCHAR2 IS -- Declare local return variable(s). lv_statement VARCHAR2(200); lv_sequence_name VARCHAR2(30); lv_return_value NUMBER := 0; -- Declare local system reference cursor. lv_cursor SYS_REFCURSOR; BEGIN -- Dynamically find sequence. lv_statement := 'SELECT sequence_name'||CHR(10) || 'FROM user_sequences'||CHR(10) || 'WHERE sequence_name = :seq_name'; OPEN lv_cursor FOR lv_statement USING DBMS_ASSERT.SIMPLE_SQL_NAME(pv_sequence_name); FETCH lv_cursor INTO lv_sequence_name; CLOSE lv_cursor; -- Convert valid sequence name to positive integer, which represents truth. lv_return_value := LENGTH(lv_sequence_name); -- Return value. RETURN lv_return_value; EXCEPTION -- Reached when DBMS_ASSERT check fails. WHEN OTHERS THEN RETURN lv_return_value; END find_sequence; -- Finds the next sequence value. FUNCTION find_next_sequence ( pv_table_name VARCHAR2 ) RETURN VARCHAR2 IS -- Declare local return variable(s). lv_statement VARCHAR2(200); lv_sequence_value NUMBER; lv_return_value NUMBER := 1; -- Declare local system reference cursor. lv_cursor SYS_REFCURSOR; BEGIN -- Dynamically find sequence. lv_statement := 'SELECT MAX('||DBMS_ASSERT.SIMPLE_SQL_NAME(pv_table_name)||'_ID) + 1'||CHR(10) || 'FROM '||DBMS_ASSERT.SIMPLE_SQL_NAME(pv_table_name); OPEN lv_cursor FOR lv_statement; FETCH lv_cursor INTO lv_sequence_value; CLOSE lv_cursor; -- Assign the return value from the NDS statement to a local return variable. lv_return_value := lv_sequence_value; -- Return value. RETURN lv_return_value; EXCEPTION -- Reached when DBMS_ASSERT check fails. WHEN OTHERS THEN RETURN lv_return_value; END find_next_sequence; -- Set precompiler instruction to run in a discrete process. PRAGMA AUTONOMOUS_TRANSACTION; BEGIN -- Conditionally drop sequence. drop_sequence(DBMS_ASSERT.SIMPLE_SQL_NAME(pv_sequence_name)); -- Create sequence. create_sequence(DBMS_ASSERT.SIMPLE_SQL_NAME(pv_sequence_name), pv_cache_value); END; / |
You can test this procedure with the following script, which includes COMMIT statements. Those are requires because the stand alone procedure runs independently of the current session as an autonomous procedure.
-- Conditionally drop existing tables and sequences. BEGIN FOR i IN (SELECT object_name, object_type FROM user_objects WHERE object_name IN ('SAMPLE','SAMPLE_S')) LOOP IF i.object_type = 'TABLE' THEN EXECUTE IMMEDIATE 'DROP TABLE '||i.object_name||' CASCADE CONSTRAINTS'; dbms_output.put_line(i.object_name); ELSIF i.object_type = 'SEQUENCE' THEN EXECUTE IMMEDIATE 'DROP SEQUENCE '||i.object_name; dbms_output.put_line(i.object_name); END IF; END LOOP; END; / -- Create test table. CREATE TABLE sample (sample_id NUMBER); -- Create test table. CREATE SEQUENCE sample_s; -- Insert a seeding row. INSERT INTO sample VALUES (10); -- Commit the values because the procedure is autonomous. COMMIT; -- Reset the sequence value. EXECUTE reset_sequence('SAMPLE','SAMPLE_S'); -- Insert the next sequence value. INSERT INTO sample VALUES (sample_s.nextval); -- Commit the values because the procedure is autonomous. COMMIT; -- Query the result to ensure the numbers are sequential. SELECT * FROM sample; EXECUTE reset_sequence('SAMPLE','SAMPLE_S',500); -- Insert the next sequence value. INSERT INTO sample VALUES (sample_s.nextval); -- Query the result to ensure the numbers are sequential. SELECT * FROM sample; |
Hope this helps anybody interested in automating the process of resetting a START WITH value of an Oracle sequence.
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