MySQL has built index queries very slowly

Tag: Requires name MYSQ port to cause view query detection EPO

Encountered a problem, there are several structure of a query, the index of the table is also built, but some queries quickly, some are very slow, it takes more than half a minute to execute.

There's no difference between viewing the execution plan. For a long time it was discovered that the character encoding of the table involved in the main query and subquery is inconsistent. The problem is resolved after the consistency is changed.

SQL is as follows:

Delete  from WHERE  not inch (SELECT from T_diag_reportinfo)

The reason is that the character encoding of the T_diag_detection table is UTF8MB4, and the character encoding of the T_diag_reportinfo table is UTF8. This was the case when the migration database was not noticed.

After the character encoding has been changed to utf8, less than 1s is done, a total of tens of thousands of data.

MySQL has built index queries very slowly