mysql優化2-exists用法及order by及慢日誌查詢

  exists 的用法 select * from t where t.deptId in (select id from s)   等於 select * from t where exists (select 1 from s where s.id=t.deptId)   order by   慢日誌查詢（ show global status like '%Slow_queries%';查

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