mysql条件语句？

Question

我在sql查询中遇到了一个小问题，

下面是查询

SELECT events.event_id,
( SELECT favorite_events.event_id, 
        (CASE favorite_events.event_id WHEN NULL THEN 0 ELSE 1 END)
        FROM favorite_events 
        WHERE favorite_events.event_id = events.event_id 
) AS is_favorite
FROM events 
WHERE start_date = 2013-07-16

它给了我“操作数应该包含1列”错误，请帮助！

Answer 1

使用联接，而不是相关子查询。

SELECT e.event_id,
       f.event_id IS NOT NULL AS is_favorite
FROM events e
LEFT JOIN favorite_events f
ON f.event_id = e.event_id
WHERE e.start_date = '2013-07-16'

Answer 2

在子查询中，您将选择2列。不能将2个列重命名为is_favorite。

我假设，通过查看查询，您可能不需要字段favorite_events.event_id。去掉那部分就行了。