SQL申請合計平均有條件

Question

假定我們如下表具有：

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

如何可以總結（值）時索引= 1個或索引= 3，並且平均（值）當索引= 2的一個選擇聲明？

Answer 1

輕鬆：

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