例如 A LEFT JOIN B 中A是主标还是字表
Questions about the main table and sub-tables of LEFT JOIN? - PHP Chinese website Q&A - Questions about the main table and sub-tables of LEFT JOIN? - PHP Chinese website Q&A
Take a look around and learn.
A是左表，B相当于子表，查询时A表全部内容都显示，B表中只会显示和A表中有交集的部分，B表不一定会全部显示
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Questions about the main table and sub-tables of LEFT JOIN? - PHP Chinese website Q&A - Questions about the main table and sub-tables of LEFT JOIN? - PHP Chinese website Q&A
Take a look around and learn.
A是左表，B相当于子表，查询时A表全部内容都显示，B表中只会显示和A表中有交集的部分，B表不一定会全部显示