有条件地加入mysql

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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'