mysql如何加入表 [英] Mysql how to join tables

问题描述

我有三个表:

• 表1包含一个主键.
• 表2所包含的外键等于表1的主键.
• 表3所包含的外键等于表2的主键.

问题:是否可以仅知道表1的主键而从表2和3中选择信息?如果是这样，请简要说明一下选择查询".我尝试进行内部联接，但是出现语法错误.

QUESTION: Is it possible to SELECT information from table 2 and 3 while only knowing the primary key of table 1? If so please give a brief example of the SELECT QUERY. I have tried doing an Inner join but got a syntax error.

推荐答案

是的.

示例:

table_a              table_b             table_c
 _______________      _______________     _______________
|  id  |  name  |    |  id  | gender |   |  id  |   age  |
|------+--------|    |------+--------|   |------+--------|
|   1  |  sam   |    |   1  |    m   |   |   1  |   18   |
|------+--------|    |------+--------|   |------+--------|
|   2  |  ana   |    |   2  |    f   |   |   2  |   22   |
|------+--------|    |------+--------|   |------+--------|

为了获得以下结果:

 _________________________________ 
|  id  |  name  | gender |   age  |
|------+--------+--------+--------|
|   1  |  sam   |    m   |   18   |
|------+--------+--------+--------|
|   2  |  ana   |    f   |   22   |

您可以使用以下SQL语句:

You could use the following SQL statement:

SELECT a.id, a.name, b.gender, c.age
FROM table_a AS a
LEFT JOIN table_b AS b
    ON a.id = b.id
LEFT JOIN table_c AS c
    ON a.id = c.id

附言:仅回答了此问题，以进行ascii art xD！

P.S.: only answered this to do the ascii art xD!

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