使用MySQL,我可以执行以下操作:

SELECT hobbies FROM peoples_hobbies WHERE person_id = 5;

我的输出:

shopping
fishing
coding

但我只想要1行1列:

预期输出:

shopping, fishing, coding

原因是我从多个表中选择了多个值,在所有的连接之后,我得到了比我想要的多得多的行。

我在MySQL Doc上查找了一个函数,它看起来不像CONCAT或CONCAT_WS函数接受结果集。

这里有人知道怎么做吗?


当前回答

现在已经很晚了,但对于那些正在搜索“使用透视表将多个MySQL行连接到一个字段中”的人来说会很有帮助:)

查询:

SELECT pm.id, pm.name, GROUP_CONCAT(c.name) as channel_names
FROM payment_methods pm
LEFT JOIN payment_methods_channels_pivot pmcp ON pmcp.payment_method_id = pm.id
LEFT JOIN channels c ON c.id = pmcp.channel_id
GROUP BY pm.id

桌子

payment_methods 
  id  | name
  1   | PayPal

channels
  id  | name
  1   | Google
  2   | Faceook

payment_methods_channels_pivot
   payment_method_id | channel_id
   1                 |  1
   1                 |  2

输出:

其他回答

您可以使用GROUP_CONCAT:

SELECT person_id,
   GROUP_CONCAT(hobbies SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;

正如Ludwig在评论中所说,您可以添加DISTINCT运算符以避免重复:

SELECT person_id,
   GROUP_CONCAT(DISTINCT hobbies SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;

正如Jan在他们的评论中所说,您也可以在使用ORDER BY将值内爆之前对其进行排序:

SELECT person_id, 
       GROUP_CONCAT(hobbies ORDER BY hobbies ASC SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;

正如Dag在评论中所说,结果有1024字节的限制。要解决此问题,请在查询之前运行此查询:

SET group_concat_max_len = 2048;

当然,您可以根据需要更改2048。要计算和分配值:

SET group_concat_max_len = CAST(
                     (SELECT SUM(LENGTH(hobbies)) + COUNT(*) * LENGTH(', ')
                           FROM peoples_hobbies
                           GROUP BY person_id) AS UNSIGNED);

连接多个单独行的替代语法

警告:这篇文章会让你饿。

鉴于:

我发现自己想要选择多个单独的行,而不是一个组,并在某个字段上进行连接。

假设您有一个产品ID及其名称和价格表:

+------------+--------------------+-------+
| product_id | name               | price |
+------------+--------------------+-------+
|         13 | Double Double      |     5 |
|         14 | Neapolitan Shake   |     2 |
|         15 | Animal Style Fries |     3 |
|         16 | Root Beer          |     2 |
|         17 | Lame T-Shirt       |    15 |
+------------+--------------------+-------+

然后,你有一些花哨的聊天ajax,将这些小狗列为复选框。

饥饿的河马用户选择13、15、16。她今天没有甜点。。。

查找:

一种用纯mysql在一行中总结用户订单的方法。

解决方案:

将GROUP_NCAT和IN子句一起使用:

mysql> SELECT GROUP_CONCAT(name SEPARATOR ' + ') AS order_summary FROM product WHERE product_id IN (13, 15, 16);

哪些输出:

+------------------------------------------------+
| order_summary                                  |
+------------------------------------------------+
| Double Double + Animal Style Fries + Root Beer |
+------------------------------------------------+

奖金解决方案:

如果您也想要总价,请输入SUM():

mysql> SELECT GROUP_CONCAT(name SEPARATOR ' + ') AS order_summary, SUM(price) AS total FROM product WHERE product_id IN (13, 15, 16);
+------------------------------------------------+-------+
| order_summary                                  | total |
+------------------------------------------------+-------+
| Double Double + Animal Style Fries + Root Beer |    10 |
+------------------------------------------------+-------+

这里,我的意图是在不使用group_concat()函数的情况下应用字符串连接:

Set @concatHobbies = '';
SELECT TRIM(LEADING ', ' FROM T.hobbies ) FROM 
(
   select 
   Id, @concatHobbies := concat_ws(', ',@concatHobbies,hobbies) as hobbies
   from peoples_hobbies
)T
Order by Id DESC
LIMIT 1

Here

   select 
   Id, @concatHobbies := concat_ws(', ',@concatHobbies,hobbies) as hobbies
   from peoples_hobbies

将返回

  Id    hobbies
  1     , shopping
  2     , shopping, fishing
  3     , shopping, fishing, coding

现在我们的预期结果是第三。所以我用

  Order by Id DESC 
  LIMIT 1
  

然后我也将第一个“,”从字符串中删除

 TRIM(LEADING ', ' FROM T.hobbies )

有一个GROUP聚合函数GROUP_CONCAT。

我们有两种方法连接MySql中的列

select concat(hobbies) as `Hobbies` from people_hobbies where 1

Or

select group_concat(hobbies) as `Hobbies` from people_hobbies where 1