如何根据IIF语句的结果选择组？

Question

让我说我有这张桌子

ID  Item    Number
1   Pork    10
2   Fish    15
3   Carrot  5
4   Tomato  5

我想按项目分组并将此组命名为“类别”，然后选择每个类别的数字总和，如下所示：

SELECT Sum(Number) AS Total,
FROM TABLE
GROUP BY IIF(Item IN ('Pork', 'Fish'), 'Meat', 'Vegetable')

但是如何获得我指定的类别名称？

Answer 1

使用

SELECT 
 (CASE WHEN ITEM IN ('Pork', 'Fish') THEN 'Meat' ELSE 'Vegetable' END) TYPE, SUM(NUMBER)
FROM TABLE
GROUP BY (CASE WHEN ITEM IN ('Pork', 'Fish') THEN 'Meat' ELSE 'Vegetable' END)

Answer 2

您也可以使用WITH声明：

WITH T1 AS 
(
SELECT IIF(Item IN ('Pork', 'Fish'), 'Meat', 'Vegetable') as Grp,
       T.*
FROM T
)

SELECT Grp,SUM(Number) as Total
FROM T1
GROUP BY Grp

SQLFiddle demo