试图在mysql中连接三个不同的行答案

【问题标题】：Trying to concatenate three different rows in mysql试图在mysql中连接三个不同的行
【发布时间】：2021-11-27 13:33:32
【问题描述】：

所以，我有一个属性表，我正在尝试构建一个查询以连接到一列

attributes
------------
id, c_id, key, value
1,  1,    'day', 11
2,  1,    'month', 09
3,  1,    'year', 1999
4,  2,    'day', 14
5,  2,    'month', 11
6,  2,    'year', 2004

这是我写的查询，

SELECT 
consumer_id,
CONCAT(
    (SELECT `value` FROM consumer_attributes WHERE `key` = 'select_day'),
    '_',
    CONCAT(
        (SELECT `value` FROM consumer_attributes WHERE `key` = 'select_month'),
        '_',
        CONCAT(
            (SELECT `value` FROM consumer_attributes WHERE `key` = 'select_year'),
            '',
            ''
        )
    )
) AS dob
FROM consumer_attributes

扔出去

错误代码：1242 子查询返回多于 1 行

有人可以帮帮我吗？

我想要达到的输出

consumer_id, concat
1, 11_09_1999
2, 14_11_2004

【问题讨论】：

标签： mysql concatenation

【解决方案1】：

另一种方法（如果您有大量数据，您可能希望对不同的答案进行计时）；

SELECT c_id, CONCAT(d.d, '_', m.m, '_', y.y) dob 
FROM (select c_id, value d FROM consumer_attributes WHERE `key`='day') d 
NATURAL JOIN (select c_id, value m FROM consumer_attributes WHERE `key`='month') m 
NATURAL JOIN (select c_id, value y FROM consumer_attributes WHERE `key`='year') y;

【讨论】：

【解决方案2】：

SELECT c_id, CONCAT_WS('_',
  (SELECT value FROM consumer_attributes a WHERE `key`='day' AND a.c_id = c.c_id),
  (SELECT value FROM consumer_attributes a WHERE `key`='month' AND a.c_id = c.c_id),
  (SELECT value FROM consumer_attributes a WHERE `key`='year' AND a.c_id = c.c_id)) AS dob
FROM (SELECT DISTINCT c_id FROM consumer_attributes) c;

https://www.db-fiddle.com/f/pB6b5xrgPKCivFWcpQHsyE/14

【讨论】：

【解决方案3】：

注意：是 select_day 还是 day ？如果它不同，您应该在查询上方更改它。

您没有将子查询与带有 id 列的主查询连接起来，因此它会为每条记录找到不止一行。其他都ok的话应该没问题：

    SELECT 
dmy.consumer_id,
concat (
max(ifnull(    (SELECT `value` FROM consumer_attributes dd WHERE `key` = 'day' and dd.id = dmy.id) , -1)) ,'_' ,
max(ifnull(        (SELECT `value` FROM consumer_attributes mm WHERE `key` = 'month' and mm.id = dmy.id)  , -1) ), '_' ,
max(ifnull(            (SELECT `value` FROM consumer_attributes yy WHERE `key` = 'year' and yy.id = dmy.id) , -1)) )
FROM consumer_attributes dmy
group by dmy.consumer_id

【讨论】：

【解决方案4】：

试试这个，

    SELECT `c_id`, CONCAT(GROUP_CONCAT(IF(`key` = 'day', `value`, NULL)),'_',GROUP_CONCAT(IF(`key` = 'month', `value`, NULL)),'_',GROUP_CONCAT(IF(`key` = 'year', `value`, NULL))) as dob
    FROM `consumer_attributes`
    GROUP BY `c_id`

【讨论】：

表中有很多其他属性，我需要指定键。