desc_t The PL/SQL table, which contains all of the column information. This is a table of records of type DBMS_SQL.DESC_REC (<table_type), which is described later. The following table lists the DBMS_SQL.DESC_REC record type fields. <table_type> Datatype Description col_type BINARY_INTEGER Type of column described col_max_len BINARY_INTEGER Maximum length of column value col_name VARCHAR2(32) Name of the column col_name_len BINARY_INTEGER Length of the column name col_schema_name VARCHAR2(32) Name of column type schema if an object type col_schema_name_len BINARY_INTEGER Length of schema name col_precision BINARY_INTEGER Precision of column if a number col_scale BINARY_INTEGER Scale of column if a number col_charsetid BINARY_INTEGER ID of character set col_charsetform BINARY_INTEGER Character set form col_null_ok BOOLEAN TRUE if column can be NULL The values for column types are as follows: Datatype Number VARCHAR2 1 NVARCHAR2 1 NUMBER 2 INTEGER 2 LONG 8 ROWID 11 DATE 12 RAW 23 LONG RAW 24 CHAR 96 NCHAR 96 MLSLABEL 106 CLOB (Oracle8) 112 NCLOB (Oracle8) 112 BLOB (Oracle8) 113 BFILE (Oracle8) 114 Object type (Oracle8) 121 Nested table Type (Oracle8) 122 Variable array (Oracle8) 123 When you call this program, you need to have declared a PL/SQL table based on the DBMS_SQL.DESC_T. You can then use PL/SQL table methods to traverse the table and extract the needed information about the [Appendix A] What's on the Companion Disk? 2.3.11 Describing Cursor Columns 81 cursor. The following anonymous block shows the basic steps you will perform when working with this built−in: DECLARE cur PLS_INTEGER := DBMS_SQL.OPEN_CURSOR; cols DBMS_SQL.DESC_T; ncols PLS_INTEGER; BEGIN DBMS_SQL.PARSE (cur, 'SELECT hiredate, sal FROM emp', DBMS_SQL.NATIVE); DBMS_SQL.DEFINE_COLUMN (cur, 1, SYSDATE); DBMS_SQL.DEFINE_COLUMN (cur, 2, 1); DBMS_SQL.DESCRIBE_COLUMNS (cur, ncols, cols); FOR colind IN 1 ncols LOOP DBMS_OUTPUT.PUT_LINE (cols.col_name); END LOOP; DBMS_SQL.CLOSE_CURSOR (cur); END; / If you are going to use this procedure to extract information about a dynamic cursor, you will likely want to build a "wrapper" around it to make it easier for you to get at this data. The Section 2.5" section at the end of this chapter offers an example of this wrapper. How'd He Get Those Numbers? The Oracle documentation for DBMS_SQL tells us only that the col_type field of the DBMS_REC record contains the "type of the column being described" and that the type is an INTEGER. Well, what exactly are those integer values? I could have sent email to someone at Oracle Corporation and waited for a response. But even then, how would I be sure that those values are correct? And why depend on another person, when I can depend on the software itself? To figure out the different column type values, I first constructed a table as follows: CREATE TABLE coltypes (vc VARCHAR2(10), nvc NVARCHAR2(10), ch CHAR(10), nch NCHAR(10), d DATE, n NUMBER, i INTEGER, l LONG, r RAW(100), rid ROWID, cl CLOB, ncl NCLOB, bl BLOB, bf BFILE, msl MLSLABEL ) / These columns pretty much cover all of the datatypes through Oracle8. I then built a script which relies on the desccols package to call the DESCRIBE_COLUMNS procedure (see the Section 2.5" section) and display the column information, including the column types. /* Filename on companion disk: desccols.xmn */ DECLARE cur integer := dbms_sql.open_cursor; [Appendix A] What's on the Companion Disk? 2.3.11 Describing Cursor Columns 82 cl CLOB; bl BLOB; ncl NCLOB; bf BFILE; msl MLSLABEL; r RAW(100); rid ROWID; BEGIN dbms_sql.PARSE (cur, 'SELECT vc, nvc, ch, nch, d, n, i, l, r, rid, cl, ncl, bl, bf, msl FROM coltypes', DBMS_SQL.NATIVE); DBMS_SQL.DEFINE_COLUMN (cur, 1, 'a', 10); DBMS_SQL.DEFINE_COLUMN (cur, 2, 'a', 10); DBMS_SQL.DEFINE_COLUMN_CHAR (cur, 3, 'a', 10); DBMS_SQL.DEFINE_COLUMN_CHAR (cur, 4, 'a', 10); DBMS_SQL.DEFINE_COLUMN (cur, 5, SYSDATE); DBMS_SQL.DEFINE_COLUMN (cur, 6, 1); DBMS_SQL.DEFINE_COLUMN (cur, 7, 1); DBMS_SQL.DEFINE_COLUMN_LONG (cur, 8); DBMS_SQL.DEFINE_COLUMN_RAW (cur, 9, r, 10); DBMS_SQL.DEFINE_COLUMN_ROWID (cur, 10, rid); DBMS_SQL.DEFINE_COLUMN (cur, 11, cl); DBMS_SQL.DEFINE_COLUMN (cur, 12, ncl); DBMS_SQL.DEFINE_COLUMN (cur, 13, bl); DBMS_SQL.DEFINE_COLUMN (cur, 14, bf); DBMS_SQL.DEFINE_COLUMN (cur, 15, msl); dyncur.desccols (cur); dyncur.show; DBMS_SQL.CLOSE_CURSOR (cur); END; / and I got this output: Column 1 VC 1 Column 2 NVC 1 Column 3 CH 96 Column 4 NCH 96 Column 5 D 12 Column 6 N 2 Column 7 I 2 Column 8 L 8 Column 9 R 23 Column 10 RID 11 Column 11 CL 112 Column 12 [Appendix A] What's on the Companion Disk? 2.3.11 Describing Cursor Columns 83 NCL 112 Column 13 BL 113 Column 14 BF 114 Column 15 MSL 106 I could then document those values with confidence in this book. I wanted to show you this so that you understand that even when a person knows an awful lot about PL/SQL, he doesn't necessarily know everything. In fact, knowing everything is completely impossible and anyone claiming to "know it all" should not be trusted. Recognize your areas of ignorance and then search out the answers, preferably by going to the source −− the source code, that is. 2.2 Getting Started with DBMS_SQL 2.4 Tips on Using Dynamic SQL Copyright (c) 2000 O'Reilly & Associates. All rights reserved. [Appendix A] What's on the Companion Disk? 2.3.11 Describing Cursor Columns 84 Chapter 2 Executing Dynamic SQL and PL/SQL 2.4 Tips on Using Dynamic SQL This section offers advice about how best to take advantage of dynamic SQL and the DBMS_SQL package. Following this section is a series of detailed examples of putting DBMS_SQL to use. 2.4.1 Some Restrictions You can do a lot of awfully interesting stuff with DBMS_SQL, but some things are off−limits: • You cannot manipulate cursor variables from within dynamic SQL. Cursor variables are a relatively new, advanced, and little−used feature of PL/SQL (see Chapter 6 of Oracle PL/SQL Programming for more information). But if you want to use them, you'll have to do it in static PL/SQL code. • Unless otherwise noted, DBMS_SQL does not support many of the new data structures in Oracle8. For example, you cannot bind an object or a nested table or a variable array. 2.4.2 Privileges and Execution Authority with DBMS_SQL There are two basic rules to remember when working with DBMS_SQL: • Stored programs execute under the privileges of the owner of that program. So if you parse and execute dynamic SQL from within a program, references to database objects in that SQL statement are resolved according to the schema of the program, not the schema of the person running the program. • Roles are disabled when compiling and executing PL/SQL code. Privileges must be granted directly in order to be used with PL/SQL code. So when you execute dynamic SQL from within a PL/SQL program, you must have directly granted privileges to any database objects referenced in the dynamically constructed string. The following anecdotes demonstrate the kinds of problems you can face with dynamic SQL. 2.4.2.1 The tale of Jan Jan is a sharp DBA. She keeps up on the latest in Oracle technology, both within her discipline and in the wider array of Oracle software. When Oracle Server Release 7.1 hit the street, she checked for new features and came across the built−in DBMS_SQL package. DBMS_SQL, she discovered, allows you to execute dynamic SQL and PL/SQL from within PL/SQL programs. Jan immediately saw the possibilities and built herself a suite of procedures to perform DBA tasks, all inside 85 . 96 MLSLABEL 106 CLOB (Oracle8 ) 112 NCLOB (Oracle8 ) 112 BLOB (Oracle8 ) 113 BFILE (Oracle8 ) 114 Object type (Oracle8 ) 121 Nested table Type (Oracle8 ) 122 Variable array (Oracle8 ) 123 When you call. in Oracle technology, both within her discipline and in the wider array of Oracle software. When Oracle Server Release 7.1 hit the street, she checked for new features and came across the built−in. the end of this chapter offers an example of this wrapper. How'd He Get Those Numbers? The Oracle documentation for DBMS_SQL tells us only that the col_type field of the DBMS_REC record contains