有条件地加入mysql [英] conditional join in mysql

问题描述

我有一个表id1，id2，type. type是包含另一个表名称的枚举值. 我想使用表type的名称来执行join. 例如:

I have a table id1, id2, type. type is an enumerated value containing a name of another table. I'd like to preform a join with the name of the table of type. For example:

switch($type)
case 'table1':
   join table1;
   break;
case 'table2':
   join table2;
   break;

我该如何实现?

推荐答案

您不能直接那样做...尽管您可以做这样的事情(不是很漂亮...):

You can't do it directly like that... you can do something like this though (not very pretty...):

SELECT
t.id,
t.type,
t2.id AS id2,
t3.id AS id3

FROM t
LEFT JOIN t2 ON t2.id = t.id AND t.type = 't2'
LEFT JOIN t3 ON t3.id = t.id AND t.type = 't3'

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