MySQL-查询-多分组依据
我有一个下表,在这个表中,我试图对type='printer'求和,但是,我不想计算重复的客户端ID。所以我期待着这样的事情:MySQL-查询-多分组依据,sql,mysql,group-by,aggregate-functions,Sql,Mysql,Group By,Aggregate Functions,我有一个下表,在这个表中,我试图对type='printer'求和,但是,我不想计算重复的客户端ID。所以我期待着这样的事情: +------+-----------+-----------+ | k_id | client_id | type | +------+-----------+-----------+ | 1 | 100 | pc | | 2 | 101 | printer | | 3 | 101
+------+-----------+-----------+
| k_id | client_id | type |
+------+-----------+-----------+
| 1 | 100 | pc |
| 2 | 101 | printer |
| 3 | 101 | printer |
| 4 | 101 | printer |
| 5 | 102 | cellphone |
+------+-----------+-----------+
查询:
SELECT client_id,
SUM(IF(type = 'printer', 1,0))
FROM FOO
GROUP BY type, client_id;
结果:
+-----------+--------------------------------+
| client_id | SUM(IF(type = 'printer', 1,0)) |
+-----------+--------------------------------+
| 102 | 0 |
| 100 | 0 |
| 101 | 3 |
+-----------+--------------------------------+
预期结果:
+-----------+--------------------------------+
| client_id | SUM(IF(type = 'printer', 1,0)) |
+-----------+--------------------------------+
| 102 | 0 |
| 100 | 0 |
| 101 | 1 |
+-----------+--------------------------------+
打印机类型为
时有三行Sum
将它们全部相加,并返回3
如果您想查看带有打印机的行的1
,或者0
,请尝试max
而不是sum
:
MAX(IF(type = 'printer', 1,0))
^^^
编辑:要计算不同打印机的数量,可以使用子查询:
SELECT client_id
, (
select count(*)
from FOO as f2
where f1.client_id = f2.client_id
and type = 'Printer'
)
FROM FOO as f1
GROUP BY
client_id
(我猜:我不熟悉IF(…)使用:
SELECT x.client_id,
COUNT(DISTINCT y.type)
FROM FOO x
LEFT JOIN FOO y ON y.client_id = x.client_id
AND y.type = 'printer'
GROUP BY x.client
如果不需要查看计数为零的行:
SELECT client_id,
COUNT(DISTINCT type)
FROM FOO
WHERE type = 'printer'
GROUP BY type, client_id;
选择客户端id,如果(`type`='printer',1,0)
来自富
按类型分组,客户端id
在mysql中,您不需要max,只需省略function@Josh:您可以使用子查询(添加到答案)@Imre L:Withoutmax()
,它将仅对随机行运行if
,而不是所有if
SELECT client_id,
COUNT(DISTINCT type)
FROM FOO
WHERE type = 'printer'
GROUP BY type, client_id;