SQL申请合计平均有条件

Question

假定我们如下表具有：

index value 
1  55 
2  66 
3  77 
1  88 
3  99 

如何可以总结（值）时索引= 1个或索引= 3，并且平均（值）当索引= 2的一个选择声明？

Answer 1

轻松：

SELECT index, CASE WHEN index IN (1, 3) THEN SUM(value) ELSE AVG(value) END 
FROM yourTable 
GROUP BY index 

Answer 2

SELECT sum(value) as agg, 
     'S' as aggregateType 
FROM DaTAble 
WHERE index IN (1, 3) 

UNION ALL 

SELECT avg(value) as agg, 
     'A' as aggregateType 
FROM DaTAble 
WHERE index = 2