,, good, I just started to learn SQL optimization,
Want to ask next: the implementation process of the execution plan="self-understanding:
A full table scan temp1 table before sorting, the scan temp table and then sorting, merged into one big table after sorting, don't know understand right , this table the execution of the plan, have bosses to teaching?

CodePudding user response:

First index search MGR in temp1=7839,

According to the above results, matching of the NL access temp2, in this case, the access temp2 NL, no use index, a full table,