MySql如果然后在Select语句中 [英] MySql If Then in Select Statement

问题描述

我想在mysql select中使用IF THEN语句，但无法弄清楚.如果尚无注释，则commentcreated值应为项目本身的创建值.这是查询:

I want to use an IF THEN statement in a mysql select, but can't figure it out. When there are no comments yet, the commentcreated value should be the created value of the item itself. This is the query:

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

我想通了，但它不起作用:

I'd figured this, but it doesn't work:

...
, IF max(comments.created)!='NULL'
THEN max(comments.created) AS commentcreated
ELSE item.created AS commentcreated
END IF;
FROM .......

(最佳)方法是什么?

推荐答案

可以使用IFNULL

IFNULL(max(comments.created), item.created) AS commentcreated

或IF

IF(max(comments.created)='NULL', max(comments.created), item.created) 
AS commentcreated

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