的MySQL与IF条件

Question

我想通过查询呈三角了一定的效果加入？

Answer 1

SELECT * FROM users 
LEFT JOIN private AS details ON users.id = details.user_id 
WHERE users.id = 1 AND users.type = 1 

UNION 

SELECT * FROM users 
LEFT JOIN company AS details ON users.id = details.user_id 
WHERE users.id = 1 AND users.type != 1 

我认为这是你正在尝试做的，不是吗？如您现在所说的列数不同，您需要指定列（例如，列）。

SELECT 'private' AS detailType, users.*, col1, col2, col3, '' FROM users 
LEFT JOIN private AS details ON users.id = details.user_id 
WHERE users.id = 1 AND users.type = 1 

UNION 

SELECT 'company', users.*, col1, '', '', col4 FROM users 
LEFT JOIN company AS details ON users.id = details.user_id 
WHERE users.id = 1 AND users.type != 1 

在这个例子中，私人拥有列COL1，COL2和COL3，同时公司拥有col1和COL4，但你希望他们所有。

Answer 2

SELECT 
    users.*, 
    details.info, 
    CASE users.type WHEN '1' THEN 'private' ELSE 'company' END AS user_type 
FROM 
    users 
    INNER JOIN (
    SELECT user_id, info FROM private 
    UNION 
    SELECT user_id, info FROM company 
) AS details ON details.user_id = users.id 

---

编辑：回答（问题误解）的原始版本：

SELECT 
    *, 
    CASE type WHEN '1' THEN 'private' ELSE 'company' END AS details 
FROM 
    users 
WHERE 
    users.id = 1 

Answer 3

我相信这已经解决了，但对于有类似问题的人。

您也可以尝试将多个左联接，以获取所有数据

SELECT *, IF (users.type = 1, p.name, c.name) AS name FROM users 
LEFT JOIN private AS p ON (users.type = 1 AND users.id = p.user_id) 
LEFT JOIN company AS c ON (users.type != 1 AND users.id = c.user_id)