Question

我试图在mySQL DB中进行查询

我有

Field 1 | Field 2 | url
v1      | Value01 | http:1
v1      | Value02 | http:2
v2      | Value02 | http:3
v3      | Value01 | http:4
v3      | Value02 | http:5
v2      | Value02 | http:6

我尝试在重复时计算字段2中的值所有按字段1分组

我期待这个

Field 1  | count Value01(from Field 2)|count Value02(from Field 2)
v1       | 1                          | 1
v2       | 0                          | 2
v3       | 1                          | 1

有没有办法做这样的事情？

Answer 1

您使用条件COUNT或SUM

您可以删除ELSE NULL因为CASE的默认回复，但我将其包含在内以便清楚阅读。

SELECT 
    Field1, 
    COUNT( CASE 
             WHEN Field2 = 'Value01' THEN 1
             ELSE  NULL
           END) as count_Value01,
    SUM  ( CASE 
             WHEN Field2 = 'Value02' THEN 1
             ELSE  0
           END) as count_Value02
FROM yourTable
GROUP BY Field1

Answer 2

您可以使用条件聚合来完成此操作。这在MySQL中特别简单：

select field1, sum(field2 = 'Value1') as NumValue01,
       sum(field2 = 'Value02') as NumValue2
from table t
group by field1;

SQL组由不同字段中的不同值组成

2 个答案: