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Home > Database > Mysql Tutorial > mysql---union和左连接的两倒面试题_MySQL

mysql---union和左连接的两倒面试题_MySQL

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Release： 2016-06-01 13:08:33
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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


source：php.cn
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