MySQL UNION-将返回的值合并到一组行中

我是MySQL新手，需要你的帮助。 我正在使用不同的WHERE子句值从同一个表中选择两组计数值，它们位于联合的两个部分中；像这样：

SELECT Count(column1) as 'RED', null as 'BLUE'
FROM TableA
Where column1 Like 'RED'
UNION
SELECT NULL, Count(column1)
FROM TableA
Where column1 Like 'BLUE'

我希望得到：

RED      BLUE
---      ----
23       55

但我真正得到的是：

RED      BLUE
---      ----
23       NULL
NULL     55

有谁能告诉我我做错了什么，我怎样才能得到我想要的答案？ 感谢您的帮助……

您是否尝试过：

SELECT Count(column1) as red, null as blue
FROM TableA Where column1 Like 'RED'
UNION
SELECT NULL as red, Count(column1) as blue
FROM TableA Where column1 Like 'BLUE' 

试试这个SQL语句

SELECT Count(A.column1) as red, Count(B.column1) as blue FROM TableA as A,  TableA as B Where A.column1 Like 'RED' AND B.column1 Like 'BLUE' 

---

对于

UNION

，这不是一个好的用例。您可以使用

SUM

和

CASE

来完成您想要做的事情。下面是使用您的查询的示例：

SELECT SUM(CASE WHEN column1 LIKE 'RED' THEN 1 ELSE 0 END) AS red_count,
SUM(CASE WHEN column1 LIKE 'BLUE' THEN 1 ELSE 0 END) AS blue_count
FROM TableA
WHERE column1 LIKE 'RED'
OR column1 LIKE 'BLUE'

---

这是您需要的查询

select
    A.colorcount RED,
    B.colorcount BLUE
from
    (select count(1) colorcount from tableA where column1='RED') A,
    (select count(1) colorcount from tableA where column1='BLUE') B
;

下面是示例数据

mysql> drop database if exists encue;
Query OK, 1 row affected (0.05 sec)

mysql> create database encue;
Query OK, 1 row affected (0.01 sec)

mysql> use encue
Database changed
mysql> create table tableA
    -> (
    ->     id int not null auto_increment,
    ->     column1 varchar(20),
    ->     primary key (id),
    ->     key (column1)
    -> );
Query OK, 0 rows affected (0.13 sec)

mysql> insert into tableA (column1) values
    -> ('RED'),('BLUE'),('BLUE'),('BLUE'),('RED'),('BLUE'),
    -> ('RED'),('BLUE'),('BLUE'),('BLUE'),('RED'),('BLUE'),
    -> ('RED'),('BLUE'),('BLUE'),('BLUE'),('RED'),('BLUE'),
    -> ('RED'),('BLUE'),('BLUE'),('BLUE'),('RED'),('BLUE'),
    -> ('RED'),('BLUE'),('BLUE'),('BLUE'),('RED'),('BLUE'),
    -> ('RED'),('BLUE'),('BLUE'),('BLUE'),('RED'),('BLUE'),
    -> ('RED'),('BLUE'),('BLUE'),('BLUE'),('RED'),('BLUE'),
    -> ('RED'),('BLUE'),('BLUE'),('BLUE'),('RED'),('BLUE'),
    -> ('RED'),('BLUE'),('BLUE'),('BLUE'),('RED'),('BLUE'),
    -> ('RED'),('BLUE'),('BLUE'),('BLUE'),('RED'),('BLUE'),
    -> ('RED'),('BLUE'),('BLUE'),('BLUE'),('RED'),('BLUE'),
    -> ('BLUE'),('BLUE'),('BLUE'),('BLUE'),('BLUE'),('BLUE'),
    -> ('BLUE'),('BLUE'),('BLUE'),('BLUE'),('BLUE'),('RED');
select count(1) colorcount,column1 from tableA group by column1;
Query OK, 78 rows affected (0.10 sec)
Records: 78  Duplicates: 0  Warnings: 0

mysql> select count(1) colorcount,column1 from tableA group by column1;
+------------+---------+
| colorcount | column1 |
+------------+---------+
|         55 | BLUE    |
|         23 | RED     |
+------------+---------+
2 rows in set (0.00 sec)

以下是您要查找的输出：

mysql> select A.colorcount RED,B.colorcount BLUE from
    -> (select count(1) colorcount from tableA where column1='RED') A,
    -> (select count(1) colorcount from tableA where column1='BLUE') B
    -> ;
+-----+------+
| RED | BLUE |
+-----+------+
|  23 |   55 |
+-----+------+
1 row in set (0.00 sec)

mysql>

试试看