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为啥下图答案给出的的子查询count(1)查询不用分组也是可以的

asked Jan 27, 2021 in Technique[技术] by 深蓝 (71.8m points)

查询每个部门的员工个数
二者的结果一样
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answered Jan 27, 2021 by 深蓝 (71.8m points)

关联子查询，子查询里边的where子句已经限定了id，此时id是唯一的，不需要group by。

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