mysql - "Every derived table must have its own alias"即使我给了他们别名

Question

我有这个查询，它从前一行的列之一(“next_line”)中选择数据，并从最近行中的不同列(“raw_line”)中选择数据。

SELECT CONCAT((SELECT `next_line` FROM `lines` ORDER BY id DESC LIMIT 1 OFFSET 1), (SELECT     
`raw_line` FROM `lines` ORDER BY id DESC LIMIT 1))

这个查询按原样工作得很好。但我想要做的是将这个输出放入最近行 *('composed_line')* 的不同列中。但是当我这样做时:

UPDATE `lines` set `composed_line`=CONCAT((SELECT `next_line` FROM `lines` ORDER BY id DESC LIMIT 
1 OFFSET 1), (SELECT `raw_line` FROM `lines` ORDER BY id DESC LIMIT 1)) ORDER BY id DESC LIMIT 1;

我收到此错误:

#1093 - You can't specify target table 'lines' for update in FROM clause 

所以我尝试了这个:

UPDATE `lines` set `composed_line`=CONCAT((SELECT `next_line` FROM (SELECT * FROM `lines` ORDER 
BY id DESC LIMIT 1 OFFSET 1) AS `alias`, (SELECT `raw_line` FROM (SELECT * FROM `lines` ORDER BY 
id DESC LIMIT 1)) AS `alias2` ORDER BY id DESC LIMIT 1

我得到了这个错误:

 #1248 - Every derived table must have its own alias 

我看不出我做错了什么 - 'alias' 和 'alias2' 不算作派生表别名吗？

非常感谢任何帮助!

Answer 1

您的内部选择还需要一个别名:

UPDATE `lines` set `composed_line`= 
CONCAT((SELECT `next_line` FROM (SELECT * FROM `lines` ORDER 
BY id DESC LIMIT 1 OFFSET 1) AS `alias`, 
(SELECT `raw_line` FROM (SELECT * FROM `lines` ORDER BY 
id DESC LIMIT 1) AS `alias3` ) AS `alias2` ORDER BY id DESC LIMIT 1

另请参阅:every derived table must have its own alias