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

使用GROUP_NCAT:

SELECT GROUP_CONCAT(hobbies) FROM peoples_hobbies WHERE person_id = 5;

其他回答

在sql server中,使用string_agg将行字段值透视为列:

select string_agg(field1, ', ') a FROM mytable 

or

select string_agg(field1, ', ') within group (order by field1 dsc) a FROM mytable group by field2

本例中另一个有趣的例子-

下面是people_hobbies示例表的结构-

DESCRIBE people_hobbies;
+---------+--------------+------+-----+---------+----------------+
| Field   | Type         | Null | Key | Default | Extra          |
+---------+--------------+------+-----+---------+----------------+
| id      | int unsigned | NO   | PRI | NULL    | auto_increment |
| ppl_id  | int unsigned | YES  | MUL | NULL    |                |
| name    | varchar(200) | YES  |     | NULL    |                |
| hby_id  | int unsigned | YES  | MUL | NULL    |                |
| hobbies | varchar(50)  | YES  |     | NULL    |                |
+---------+--------------+------+-----+---------+----------------+

该表的填充方式如下-

SELECT * FROM people_hobbies;
+----+--------+-----------------+--------+-----------+
| id | ppl_id | name            | hby_id | hobbies   |
+----+--------+-----------------+--------+-----------+
|  1 |      1 | Shriya Jain     |      1 | reading   |
|  2 |      4 | Shirley Setia   |      4 | coding    |
|  3 |      2 | Varsha Tripathi |      7 | gardening |
|  4 |      3 | Diya Ghosh      |      2 | fishing   |
|  5 |      4 | Shirley Setia   |      3 | gaming    |
|  6 |      1 | Shriya Jain     |      6 | cycling   |
|  7 |      2 | Varsha Tripathi |      1 | reading   |
|  8 |      3 | Diya Ghosh      |      5 | shopping  |
|  9 |      3 | Diya Ghosh      |      4 | coding    |
| 10 |      4 | Shirley Setia   |      1 | reading   |
| 11 |      1 | Shriya Jain     |      4 | coding    |
| 12 |      1 | Shriya Jain     |      3 | gaming    |
| 13 |      4 | Shirley Setia   |      2 | fishing   |
| 14 |      4 | Shirley Setia   |      7 | gardening |
| 15 |      2 | Varsha Tripathi |      3 | gaming    |
| 16 |      2 | Varsha Tripathi |      2 | fishing   |
| 17 |      1 | Shriya Jain     |      5 | shopping  |
| 18 |      1 | Shriya Jain     |      7 | gardening |
| 19 |      3 | Diya Ghosh      |      1 | reading   |
| 20 |      4 | Shirley Setia   |      5 | shopping  |
+----+--------+-----------------+--------+-----------+

现在,生成了一个表hobby_list,其中包含所有人的列表和每个人的爱好列表,每个爱好在一行中-

CREATE TABLE hobby_list AS
    -> SELECT ppl_id, name,
    -> GROUP_CONCAT(hobbies ORDER BY hby_id SEPARATOR "\n")
    -> AS hobbies
    -> FROM people_hobbies
    -> GROUP BY ppl_id
    -> ORDER BY ppl_id;
SELECT * FROM hobby_list;

使用GROUP_NCAT:

SELECT GROUP_CONCAT(hobbies) FROM peoples_hobbies WHERE person_id = 5;

如果您的MySQL版本(4.1)支持GROUP_CONCAT,请查看GROUP_CONNAT。有关详细信息,请参阅文档。

它看起来像:

  SELECT GROUP_CONCAT(hobbies SEPARATOR ', ') 
  FROM peoples_hobbies 
  WHERE person_id = 5 
  GROUP BY 'all';

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 |
+------------------------------------------------+-------+