Shulou(Shulou.com)06/01 Report--

In MySQL 5.7COUNT (), the total number of tables can be quickly obtained by selecting a clustered index and making an internal handler function call.

The execution plan shows: Extra:Select tables optimized away

In previous versions, the COUNT () request would normally be: scan the normal index to get this total.

6. The execution plan shows: Extra:Using index

If the clustered index is large (or the table has a large amount of data) and is not fully loaded into the buffer pool, the query mode of MySQL 5.7may be slower instead of using the original way (MySQL 5.6)

Solution: force the general index, but you still need to add WHERE conditions, otherwise it will not work.

Select count () from stock force index (idx_stock) where id > 0

Extra:using where,using index

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