mysql - 我想要查询显示表结果并仅使用 MySQL 查询

Question

表A

ID   |   NAME
-----+-------
n1   |   BLACK
n2   |   WHITE
n3   |   RED
n4   |   GREEN

表B

ID |   A_ID  |   BLABLA      |    TIME
---+---------+---------------+--------
1  |   n1    |    X          | sometime
2  |   n1    |    X          | sometime
3  |   n1    |    X          | sometime
4  |   n1    |    Y          | sometime
5  |   n1    |    Z          | sometime
6  |   n2    |    Y          | sometime
7  |   n2    |    Y          | sometime
8  |   n2    |    Y          | sometime
9  |   n3    |    X          | sometime
10 |   n3    |    Z          | sometime
11 |   n3    |    Z          | sometime
12 |   n3    |    Z          | sometime

我的问题

我想要查询显示表结果并仅使用 MySQL 查询。

表格结果

NAME       |     X    |    Y    |    Z
-----------+----------+---------+-----
BLACK      |    3     |     1   |    0
WHITE      |    0     |     3   |    0
RED        |    1     |     0   |    3
GREEN      |    0     |     0   |    0

Answer 1

SELECT 
  a.name
  , sum(CASE WHEN b.blabla LIKE 'X' THEN 1 ELSE 0 END) AS X
  , sum(CASE WHEN b.blabla LIKE 'Y' THEN 1 ELSE 0 END) AS Y
  , sum(CASE WHEN b.blabla LIKE 'Z' THEN 1 ELSE 0 END) AS Z
FROM tablea a
INNER JOIN tableb b ON (a.id = b.a_id)
GROUP BY a.name

我使用 like 而不是 =，因为 like 始终不区分大小写，而 = 则不然。
如果 blabla 是一个枚举，那么我建议使用 =。