MySQL - SELECT 中的 IF

Question

我有以下 MySQL 查询:

SELECT id, name, parent_id AS pID, 

(SELECT parent_id
FROM category
WHERE id = pID)
AS grandparent_id, 

(SELECT parent_id
FROM category
WHERE id = grandparent_id) 
AS greatgrandparent_id, 

(SELECT name
FROM category
WHERE id = pID)
AS parent, 

(SELECT name
FROM category
WHERE id = grandparent_id)
AS grandparent, 

(SELECT name
FROM category
WHERE id = greatgrandparent_id)
AS greatgrandparent

FROM category
WHERE active = '1'
HAVING grandparent IS NOT NULL
ORDER BY grandparent_id, parent_id, sort, id ASC 

当曾祖 parent 为NULL时，我希望它显示祖 parent 值。这可能吗？

我已经尝试过CASE WHEN，但一定是在某个地方出现了语法错误，因为它不断抛出错误。

Answer 1

简单的解决方案:ISNULL(曾祖 parent ，祖 parent )。