如何在mysql中的情况下进行连接[重复]

Question

我正在尝试构建以下查询，我知道语法不正确但有人可以提出任何想法吗？/解决方案？

Thanks 

SELECT * FROM table 
LEFT JOIN x ON x.id = table.id 
CASE table.nid 
WHEN 1 THEN (LEFT JOIN tablea ON tablea.id = table.nid) 
WHEN 2 THEN (LEFT JOIN tableb ON tableb.id = table.nid) 
WHEN 3 THEN (LEFT JOIN tablec ON tablec.id = table.nid) 
END 
WHERE talbe.id = "hello";

Answer 1

我不确定这是最有效/最漂亮的方法，但你可以试试这个：

SELECT CASE table.nid WHEN 1 THEN tablea.id WHEN 2 THEN tableb.id WHEN 3 THEN tablec.id end
FROM table
LEFT JOIN x ON x.id = table.id 
LEFT JOIN tablea ON tablea.id = table.nid
LEFT JOIN tableb ON tableb.id = table.nid
LEFT JOIN tablec ON tablec.id = table.nid 
WHERE talbe.id = "hello";