说几乎所有in的语句都可以转换成exists,从而提高效率.该怎么转换?
如这句:select dept_no from p_dinner_user t where t.tibco_pk in (select rowid from dinner_user t2 where to_char(creat_date,'yyyy mmdd')='0116')另:是不是exists中一定要子查询?请高人指点,谢谢!
如这句:select dept_no from p_dinner_user t where t.tibco_pk in (select rowid from dinner_user t2 where to_char(creat_date,'yyyy mmdd')='0116')另:是不是exists中一定要子查询?请高人指点,谢谢!
where exists (select 'X'from dinner_user t2 where to_char(creat_date,'yyyy mmdd')='0116' and t.tibco_pk=t2.rowid);另:是不是exists中一定要子查询?
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不尽然
表中数据量超出100W条,就能感觉得出!
查出来和这个能相等吗?或者帮我解释一下,谢谢了。