从三个表中选择数据? [英] Select data from three tables?

问题描述

如何编写SQL语句以从三个表中选择数据?

How can I write a SQL statement to select data from three tables?

推荐答案

使用联接

SELECT *
FROM table_1
JOIN table_2 ON (table_2.table_1_id = table_1.table_1_id)
JOIN table_3 ON (table_3.table_1_id = table_1.table_1_id)

这将要求每个表都有一个table_1_id键，并且每个表中都必须有一个条目.

This will require that each table has a table_1_id key and that there is an entry in each table.

如果table_2或table_3可能没有数据，但您仍想显示来自table_1的数据，则可以使用LEFT JOIN

You can use a LEFT JOIN if table_2 or table_3 may not have data but you still want to show the data from table_1

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