MySQL database optimization Overview 4 _ MySQL

MySQL database optimization Overview 4 table type possible_keys key key_len ref rows Extra

Tt ALL AssignedPC NULL 3872 Using
ClientID, where
ActualPC
Et eq_ref PRIMARY 15 tt. ActualPC 1
Et_1 eq_ref PRIMARY 15 tt. AssignedPC 1
Do eq_ref PRIMARY 15 tt. ClientID 1

Note that the value of the rows field in the EXPLAIN result is also roughly guessed by the MySQL connection optimization program. check whether the value is basically the same as the actual value. If not, you can use STRAIGHT_JOIN in the SELECT statement to achieve better performance.

List tables in different order in a clause