EXECUTE IMMEDIATE is the replacement for DBMS_SQL package from Oracle 8i onwards. It parses and immediately executes a dynamic SQL statement or a PL/SQL block created on the fly. Dynamically created and executed SQL statements are performance overhead, EXECUTE IMMEDIATE aims at reducing the overhead and give better performance. It is also easier to code as compared to earlier means. The error messages generated when using this feature are more user friendly. Though DBMS_SQL is still available, it is advisable to use EXECUTE IMMEDIATE calls because of its benefits over the package.
1. EXECUTE IMMEDIATE will not commit a DML transaction carried out and an explicit commit should be done.
If the DML command is processed via EXECUTE IMMEDIATE, one needs to explicitly commit any changes that may have been done before or as part of the EXECUTE IMMEDIATE itself. If the DDL command is processed via EXECUTE IMMEDIATE, it will commit all previously changed data.
2. Multi-row queries are not supported for returning values, the alternative is to use a temporary table to store the records (see example below) or make use of REF cursors.
3. Do not use a semi-colon when executing SQL statements, and use semi-colon at the end when executing a PL/SQL block.
Example of EXECUTE IMMEDIATE usage
1. To run a DDL statement in PL/SQL.
begin execute immediate 'SET ROLE ALL EXCEPT dw_manager;'; end;
2. To pass values to a dynamic statement (USING clause).
declare l_depnam varchar2(20) := 'dbareftest'; l_loc varchar2(10) := 'India'; begin execute immediate 'insert into dept values (:1, :2, :3)' using 50, l_depnam, l_loc; commit; end;
3. To retrieve values from a dynamic statement (INTO clause).
declare l_cnt varchar2(20); begin execute immediate 'select count(1) from emp' into l_cnt; dbms_output.put_line(l_cnt); end;
4. To call a routine dynamically: The bind variables used for parameters of the routine have to be specified along with the parameter type. IN type is the default, others have to be specified explicitly.
declare l_routin varchar2(100) := 'dbrefproc1.get_rowcnt'; l_tblnam varchar2(20) := 'emp'; l_cnt number; l_status varchar2(200); begin execute immediate 'begin ' || l_routin || '(:2, :3, :4); end;' using in l_tblnam, out l_cnt, in out l_status; if l_status != 'OK' then dbms_output.put_line('error'); end if; end;
5. To return value into a PL/SQL record type: The same option can be used for %rowtype variables also.
declare type empdtlrec is record (empno number(4), ename varchar2(20), deptno number(2)); empdtl empdtlrec; begin execute immediate 'select empno, ename, deptno ' || 'from emp where empno = 7934' into empdtl; end;
6. To pass and retrieve values: The INTO clause should precede the USING clause.
declare l_dept pls_integer := 20; l_nam varchar2(20); l_loc varchar2(20); begin execute immediate 'select dname, loc from dept where deptno = :1' into l_nam, l_loc using l_dept ; end;
7. Multi-row query option. Use the insert statement to populate a temp table for this option. Use the temporary table to carry out further processing. Alternatively, you may use REF cursors to by-pass this drawback.
declare l_sal pls_integer := 2000; begin execute immediate 'insert into temp(empno, ename) ' || ' select empno, ename from emp ' || ' where sal > :1' using l_sal; commit; end;
EXECUTE IMMEDIATE is a much easier and more efficient method of processing dynamic statements than could have been possible before. As the intention is to execute dynamic statements, proper handling of exceptions becomes all the more important. Care should be taken to trap all possible exceptions.
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