Connection sequence in the WHERE clause of Oracle performance optimization learning notes

Connection sequence in the WHERE clause of Oracle performance optimization learning notes

ORACLE uses the bottom-up sequence to parse the WHERE clause. According to this principle, the join between tables must be written before other WHERE conditions. The conditions that can filter out the maximum number of records must be written at the end of the WHERE clause.

For example:
(Inefficient, execution time: 156.3 seconds)

SELECT... From emp ewhere sal> 50000AND JOB = 'manager' AND 25 <(select count (*) from emp where mgr = E. EMPNO );

(Efficient, execution time: 10.6 seconds)

SELECT... From emp ewhere 25 <(select count (*) from emp where mgr = E. EMPNO) and sal> 50000AND JOB = 'manager ';

Note:
This article is taken from Baidu Library. The specific link is found. Sorry.