我需要运行如下查询：
SELECT p.id, p.name,
(SELECT name
FROM sites s
WHERE s.id = p.site_id) AS site_list
FROM publications p
但我希望子选择返回一个逗号分隔的列表，而不是一列数据。这甚至可能吗？如果可以，怎么做？
【问题讨论】：
标签： sql mysql concatenation
您可以使用GROUP_CONCAT 来执行此操作，例如像
SELECT p.id, p.name, GROUP_CONCAT(s.name) AS site_list
FROM sites s
INNER JOIN publications p ON(s.id = p.site_id)
GROUP BY p.id, p.name;
【讨论】：
GROUP_CONCAT(CAST(s.name AS CHAR))，否则它将返回完全无用的内容，例如[BLOB - 20 Bytes]。
您可以只使用concat() 而不是group concat()
Select concat(Col1, ',', Col2) as Foo_Bar from Table1;
edit 这仅适用于 mySQL； Oracle concat 只接受两个参数。在 oracle 中，您可以使用类似 select col1||','||col2||','||col3 as foobar from table1; 在 sql server 中，您将使用 + 而不是管道。
【讨论】：
在我的情况下，我必须连接一个手机号码唯一的人的所有帐号。所以我使用以下查询来实现这一点。
SELECT GROUP_CONCAT(AccountsNo) as Accounts FROM `tblaccounts` GROUP BY MobileNumber
查询结果如下：
Accounts
93348001,97530801,93348001,97530801
89663501
62630701
6227895144840002
60070021
60070020
60070019
60070018
60070017
60070016
60070015
【讨论】：
现在只有我遇到这种情况，在GROUP_CONCAT周围发现了一些更有趣的功能。我希望这些细节会让你觉得有趣。
简单的 GROUP_CONCAT
SELECT GROUP_CONCAT(TaskName)
FROM Tasks;
结果：
+------------------------------------------------------------------+
| GROUP_CONCAT(TaskName) |
+------------------------------------------------------------------+
| Do garden,Feed cats,Paint roof,Take dog for walk,Relax,Feed cats |
+------------------------------------------------------------------+
GROUP_CONCAT 与 DISTINCT
SELECT GROUP_CONCAT(TaskName)
FROM Tasks;
结果：
+------------------------------------------------------------------+
| GROUP_CONCAT(TaskName) |
+------------------------------------------------------------------+
| Do garden,Feed cats,Paint roof,Take dog for walk,Relax,Feed cats |
+------------------------------------------------------------------+
GROUP_CONCAT 与 DISTINCT 和 ORDER BY
SELECT GROUP_CONCAT(DISTINCT TaskName ORDER BY TaskName DESC)
FROM Tasks;
结果：
+--------------------------------------------------------+
| GROUP_CONCAT(DISTINCT TaskName ORDER BY TaskName DESC) |
+--------------------------------------------------------+
| Take dog for walk,Relax,Paint roof,Feed cats,Do garden |
+--------------------------------------------------------+
GROUP_CONCAT 与 DISTINCT 和 SEPARATOR
SELECT GROUP_CONCAT(DISTINCT TaskName SEPARATOR ' + ')
FROM Tasks;
结果：
+----------------------------------------------------------------+
| GROUP_CONCAT(DISTINCT TaskName SEPARATOR ' + ') |
+----------------------------------------------------------------+
| Do garden + Feed cats + Paint roof + Relax + Take dog for walk |
+----------------------------------------------------------------+
GROUP_CONCAT 和组合列
SELECT GROUP_CONCAT(TaskId, ') ', TaskName SEPARATOR ' ')
FROM Tasks;
结果：
+------------------------------------------------------------------------------------+
| GROUP_CONCAT(TaskId, ') ', TaskName SEPARATOR ' ') |
+------------------------------------------------------------------------------------+
| 1) Do garden 2) Feed cats 3) Paint roof 4) Take dog for walk 5) Relax 6) Feed cats |
+------------------------------------------------------------------------------------+
GROUP_CONCAT 和分组结果
假设以下是使用GROUP_CONCAT之前的结果
+------------------------+--------------------------+
| ArtistName | AlbumName |
+------------------------+--------------------------+
| Iron Maiden | Powerslave |
| AC/DC | Powerage |
| Jim Reeves | Singing Down the Lane |
| Devin Townsend | Ziltoid the Omniscient |
| Devin Townsend | Casualties of Cool |
| Devin Townsend | Epicloud |
| Iron Maiden | Somewhere in Time |
| Iron Maiden | Piece of Mind |
| Iron Maiden | Killers |
| Iron Maiden | No Prayer for the Dying |
| The Script | No Sound Without Silence |
| Buddy Rich | Big Swing Face |
| Michael Learns to Rock | Blue Night |
| Michael Learns to Rock | Eternity |
| Michael Learns to Rock | Scandinavia |
| Tom Jones | Long Lost Suitcase |
| Tom Jones | Praise and Blame |
| Tom Jones | Along Came Jones |
| Allan Holdsworth | All Night Wrong |
| Allan Holdsworth | The Sixteen Men of Tain |
+------------------------+--------------------------+
USE Music;
SELECT ar.ArtistName,
GROUP_CONCAT(al.AlbumName)
FROM Artists ar
INNER JOIN Albums al
ON ar.ArtistId = al.ArtistId
GROUP BY ArtistName;
结果：
+------------------------+----------------------------------------------------------------------------+
| ArtistName | GROUP_CONCAT(al.AlbumName) |
+------------------------+----------------------------------------------------------------------------+
| AC/DC | Powerage |
| Allan Holdsworth | All Night Wrong,The Sixteen Men of Tain |
| Buddy Rich | Big Swing Face |
| Devin Townsend | Epicloud,Ziltoid the Omniscient,Casualties of Cool |
| Iron Maiden | Somewhere in Time,Piece of Mind,Powerslave,Killers,No Prayer for the Dying |
| Jim Reeves | Singing Down the Lane |
| Michael Learns to Rock | Eternity,Scandinavia,Blue Night |
| The Script | No Sound Without Silence |
| Tom Jones | Long Lost Suitcase,Praise and Blame,Along Came Jones |
+------------------------+----------------------------------------------------------------------------+
【讨论】：