SQL Performance Optimization-Typical Case 3

Sometimes, when writing SQL statements, you may forget to associate tables. This is very slow, and the results are not necessarily desired.

We can find some clues Through the execution plan. For example, traversal tables consume very little, but Cartesian join is performed on the two tables, and the consumption is very large. This is to check whether the table is normally associated.

Example:

Select distinct T. exportno, t1.cocode, t2.chnname from t_enterprises T, Region T1, stdw. d_t_customer T2 where T. crmno = t1.customno and T. isdel = '0' and t1.state = '1'

Execution Plan: