mysql - SQL 中的 IF/CASE 语句

Question

我真的很难找到这个问题的答案。我想编写一个 if 或 case 语句来更改另一列中的值。如果“check”列为 0，则“points”列也应为 0。

SELECT club_name, COALESCE(club_winner,0) AS 'check', COUNT(*) AS points,
    CASE 
    WHEN check = '0'
    THEN points = '0'
    ELSE check 
    END as Saleable
    FROM clubs c
    LEFT JOIN club_results cr ON c.club_id = cr.club_winner
    GROUP BY club_name ORDER BY points DESC

Answer 1

您不能在 case 语句中“设置”列，您可以返回值。将 case 语句视为可变列。返回 '​​0' AS Saleable(或您希望命名的任何列)。

SELECT club_name, COALESCE(club_winner,0) AS 'check', COUNT(*) AS points,
CASE 
WHEN COALESCE(club_winner,0) = 0
THEN 0
ELSE COUNT(*)
END AS points_or_0_if_check_is_0
FROM clubs c
LEFT JOIN club_results cr ON c.club_id = cr.club_winner
GROUP BY club_name ORDER BY points_or_0_if_check_is_0 DESC