EXISTS是判断是否存在,和in类似,但效率要比in高
SELECT*FROMEMP(基础表)WHEREEMPNO>0ANDEXISTS(SELECT‘X'FROMDEPTWHEREDEPT.DEPTNO=EMP.DEPTNOA等争间NDLOC=‘MELB')
SELECT*FROMEMP(基础表)WHEREEMPNO>0ANDDEPT微慢坐练旧字素NOIN(SELECTDEPTNOFROMDEPTWHERELOC=‘MELB')
这两句效果一样
SQL中EXISTS怎么用
jacky
2023-11-23 09:53
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