sql inner join的本質並不是是取交集， 而是(可帶條件地)膨脹/擴張

       先看看兩張表：mysql mysql> select * from black1; +----------+ | id | +----------+ | zhangsan | | lisi | | wangwu | +----------+ 3 rows in set (0.00 sec) mysql> select * from black2; +-----

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