Question

这是我的数据

COUNTYID POLLUTANT TYPE EMISSION
1        A         1  
1        A         2
1        B         1
1        B         2
2        A         1
2        A         2  
2        B         1 
2        B         2
3        A         1
3        A         2
3        B         1 
3        B         2

如果我这样做

SELECT sum(EMISSION) from table where POLLUTANT = 'A' group by COUNTYID;

我会受到Polutant＆A 39的污染。如何编写查询以获取以下数据：

第1列，总和为A，第2列为B的总和，第3列为A和B的总和？

谢谢

Answer 1

您可以使用大小写来过滤您需要的值

  select COUNTYID, sum(case when POLLUTANT='A'then EMISSION else 0 END)  tot_a
   , sum(case when POLLUTANT='B'then EMISSION else 0 END)  tot_b
   , sum(EMISSION)  tot_a_b
  from my_table 
  group by COUNTYID

Answer 2

您可以使用条件聚合。这会将过滤条件从where子句移动到sum() s：

select countyid,
       sum(case when emission = 'A' then emission else 0 end) as A,
       sum(case when emission = 'B' then emission else 0 end) as B,
       sum(emission) as total
from t
group by countyid;

Answer 3

我想提出一些想法。我们可以使用数据透视表来回答您的问题

SELECT * from  dbo.[Table_1]
PIVOT
(Sum([type_emmssion]) for [polutant] in ([A], [B]) ) as PivotTable
 group by  [CountryId]  ;

Answer 4

你必须使用case statemet：

SELECT 
 SUM( CASE WHEN POLLUTANT = 'A' THEN EMISSION ELSE 0 END) AS A_EMISSION
 SUM( CASE WHEN POLLUTANT = 'B' THEN EMISSION ELSE 0 END) AS B_EMISSION
 SUM(EMISSION) AS total_emission
FROM table 
GROUP BY COUNTYID;

SQL中两个不同组的条件聚合

4 个答案: