在 SELECT 中使用时 CASE 'NOT NULL' 的 mysql 语法

Question

我尝试在 SELECT 语句中使用 CASE 'NOT NULL'，但我不断收到此错误消息:

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax

SELECT 
        u.id,
                CASE  ph.thumbsize WHEN NULL THEN ph.thumbsize ELSE 'defaultpicture.jpg'

            FROM
            user u  
            LEFT OUTER JOIN
                list_photos ph
        ON 
                u.id = ph.userId;

我还尝试了 CASE 这些不同的格式:

(CASE WHEN ph.thumbsize IS NOT NULL THEN 'ph.thumbsize' ELSE
 'defaultpicture.jpg')as picture       

           CASE WHEN ph.thumbsize IS NOT NULL THEN ph.thumbsize ELSE defaultpicture.jpg

Answer 1

除其他小问题外，您还缺少 END。尝试:

SELECT 
    u.id,
    CASE WHEN (ph.thumbsize IS NULL) THEN 
        'defaultpicture.jpg'
    ELSE
        ph.thumbsize
    END AS picture
FROM
    user u  
LEFT OUTER JOIN
    list_photos ph
ON 
    u.id = ph.userId;