sql語句in

  在今天之前sql一直用in語句,知道今天遇到一張數據量很大的表查了三分鍾才查出來,這才意識到數據庫優化有多重要.作為一名開發人員,首先從優化sql語句開始。

  之前用in寫sql是這樣的

select * from m_package where userId in(  select id from sys_user where newDorm='2號樓' and `newRoomNumber` = 'N413') ;

執行結果：/* 0 rows affected, 18 rows found. Duration for 1 query: 0.407 sec. */ 

  exists寫sql語句

select * from m_package as pack where
 exists (select id from sys_user as user where newDorm='2號樓' and `newRoomNumber` = 'N413' and pack.userId = user.id);

執行結果：/* 0 rows affected, 18 rows found. Duration for 1 query: 0.297 sec. */ 

inner join寫sql語句

select * from m_package as pack inner join sys_user as user where pack.userId = user.id and newDorm='2號樓' and `newRoomNumber` = 'N413';

執行結果：/* 0 rows affected, 18 rows found. Duration for 1 query: 0.234 sec. */ 

可以看出來執行效率 inner join > exists > in