Mysql 子查询只返回一个值
我有这个疑问Mysql 子查询只返回一个值,mysql,sql,Mysql,Sql,我有这个疑问 SELECT d.gid, d.channel_id FROM channels, ( SELECT gigs.id as gid, gigs.channel_id FROM gigs ORDER BY gigs.id DESC LIMIT 1 ) as d WHERE d.channel_id = channels.id LIMIT 10 我希望为每个channels.id获得一个gid,但它只返回一列。为什么呢 工作台 +---
SELECT
d.gid, d.channel_id
FROM channels, (
SELECT
gigs.id as gid, gigs.channel_id
FROM gigs
ORDER BY gigs.id DESC
LIMIT 1
) as d
WHERE d.channel_id = channels.id
LIMIT 10
我希望为每个channels.id
获得一个gid
,但它只返回一列。为什么呢
工作台
+---------+------------+
| id | channel_id |
+---------+------------+
| 150661 | 6 |
| 745797 | 6 |
| 483996 | 6 |
| 3407209 | 6 |
| 1175022 | 5 |
| 3238459 | 6 |
| 711413 | 5 |
| 524758 | 5 |
| 154764 | 5 |
| 1594779 | 5 |
| 1659091 | 2 |
| 1086768 | 6 |
| 1161320 | 8 |
| 467394 | 5 |
| 2877040 | 8 |
| 2705821 | 6 |
| 1881747 | 5 |
| 901902 | 1 |
| 143322 | 6 |
| 671658 | 1 |
+---------+------------+
通道表
+----+
| id |
+----+
| 1 |
| 2 |
| 3 |
| 4 |
| 5 |
| 6 |
| 7 |
| 8 |
| 9 |
| 10 |
+----+
试试这个
SELECT a.id, b.max_ID
FROM channels a
INNER JOIN
(
SELECT channel_ID, MAX(id) max_ID
FROM gigs
GROUP BY channel_ID
) b ON a.id = b.channel_ID
基本上,我使用
internaljoin
只显示channels
表中的id,该id在gigs
表中至少有记录。如果您想显示列表,即使在gigs
表上没有匹配项,您也应该使用LEFT JOIN
。同样,查询只返回一个结果,而不是10。哦,我忘了提一下,您需要删除GROUP BY
子句,因为您没有聚合任何列。运行大约需要8秒,这有点慢。这是解释输出。你能提供你的问题的样本记录吗德苏尔。我添加了一个更简单的查询和一些示例数据,只有当我只需要gigs.id
时,这些数据才会起作用。我需要gigs.id
和gigs.channel\u id
,这就是我使用内部选择的原因。
SELECT id, (SELECT id FROM Gigs WHERE channel_id = c.id ORDER BY id DESC LIMIT 1) As GigID
FROM channels c