Oracle Magazine, July/August 2019
Database Developer and DBA ETL Id Operation Name Rows Bytes Cost CPU Time 0 SELECT STATEMENT 1 39 5 20 00 00 01 1 HASH GROUP BY 1 39 5 20 00 00 01 2 NESTED LOOPS 1 39 4 0 00 00 01 3 NESTED LOOPS 5 39 4 0 00 00 01 4 TABLE ACCESS FULL EMPLOYEES 5 95 3 0 00 00 01 5 INDEX RANGE SCAN JHIST_ EMPLOYEE_ IX 1 0 0 00 00 01 6 TABLE ACCESS BY INDEX ROWID JOB_ HISTORY 1 20 1 0 00 00 01 ORACLE MAGAZINE JULY AUGUST 2019 138 Predicate Information identified by operation id 4 filter EXTRACT YEAR FROM INTERNAL_ FUNCTION E HIRE_ DATE 1985 5 access E EMPLOYEE_ ID J EMPLOYEE_ ID 6 filter J START_ DATE E HIRE_ DATE AND Unfortunately using EXPLAIN PLAN for tuning is the single most common mistake made by database developers Even in the earliest releases of the Oracle Database cost based optimizer there was the potential to not get to the true plan for the SQL statement execution because The developer is potentially running an EXPLAIN PLAN command in an optimizer environment not identical to the application runtime environment The
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