是否可以使用MySQL以这种方式对行进行分组？

Question

我有一个MySQL表,如:

ID, USER, PARAM, VAL
--------------------
1 | 1 | NAME | ADAM
2 | 1 | AGE  | 15
3 | 2 | NAME | EVA
4 | 2 | AGE  | 16
5 | 3 | NAME | CRISS
6 | 3 | AGE  | 14

而且我很好奇是否有一个查询会给我类似的东西:

1 | ADAM | 15
2 | EVE  | 16
3 | CRISS| 14

到目前为止,我只是使用下面的查询并在循环中对记录进行分组.

SELECT * FROM table WHERE PARAM ='NAME' OR PARAM = 'AGE'

我尝试使用GROUP但没有成功.

Answer 1

在同一个表上使用join:

SELECT a.USER user_id, a.VAL user_name, b.VAL user_age
FROM `table` a
INNER JOIN `table` b ON a.USER = b.USER
WHERE a.PARAM = 'NAME'
AND b.PARAM = 'AGE'

结果:

user_id     user_name   user_age
1           ADAM        15
2           EVA         16
3           CRISS       14

Answer 2

没有必要使用JOIN.试试这个:

SELECT USER,
       MAX(CASE PARAM WHEN 'NAME' THEN VAL ELSE NULL END) AS NAME,
       MAX(CASE PARAM WHEN 'AGE' THEN VAL ELSE 0 END) AS AGE
FROM test 
GROUP BY USER;

Answer 3

您可以使用最常用的技术生成数据透视视图

select
user,
max(case when param = 'NAME' then val end) as name,
max(case when param = 'AGE' then val end) as age
from mytable
group by user

Answer 4

你可以这样做一个查询:

SELECT t1.user,
        (
           SELECT val FROM tab1 t2 
           WHERE t2.user = t1.user 
             AND t2.param = 'Name'
        ) name,
        (
           SELECT val FROM tab1 t2 
           WHERE t2.user = t1.user 
             AND t2.param = 'Age'
        ) age
    FROM tab1 t1
    GROUP BY user

另一种可能性是group_concat,但是你可以在一列中监听所有值.

SELECT user, group_concat(param, ':', val)
    FROM tab1
    GROUP BY user