我想在 mysql select 中使用 IF THEN 语句，但无法弄清楚。当还没有评论时，commentcreated 值应该是该项目本身的创建值。这是查询：
SELECT item.*,
count(comments.itemid) AS commentcount,
max(comments.created) AS commentcreated
FROM table_items AS item
LEFT JOIN table_comments AS comments ON (comments.itemid = item.id)
WHERE item.published=1
GROUP BY item.id
ORDER BY item.created DESC
我想到了这一点，但它不起作用：
...
, IF max(comments.created)!='NULL'
THEN max(comments.created) AS commentcreated
ELSE item.created AS commentcreated
END IF;
FROM .......
做这个的最好方式是什么？
Can use IFNULL
IFNULL(max(comments.created), item.created) AS commentcreated
OR IF
IF(max(comments.created)='NULL', max(comments.created), item.created)
AS commentcreated
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