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mysql---union和左连接的两倒面试题_MySQL

WBOY
WBOYOriginal
2016-06-01 13:08:331982browse

第一道:


思路:无非是将hid与gid与t表中的tname关联起来。实质上是三表关联(m,t,t)

先将hid与tname关联起来,运用左连接


再将结果集与t表中的tname关联起来,使得gid与tname关联起来


再限定时间范围就可以得出最终结果



第二道:



思路:题目的要求是将相同id的值进行求和

我们可以先union all一下


再利用sum函数分组求和


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