MySQL Statement optimization tips

• When using the group by group query, the default grouping is also sorted (using Filesort) and may slow down.

Workaround: Add order by NULL to not sort it

Select *  from Group  by Empno  orderbynull;

• In some cases, you can use a connection to replace a subquery. Because using Join,mysql does not require the creation of temporary tables in memory

Select *  from where dept.deptno=[ simple processing mode ]Select* from  Left Join  on Dept.deptno=Emp.deptno;  [ left outer connection, more ok! ]

MySQL Statement optimization tips