Question

我们说我有一个这样的表，称为库存：

**Fruit**        **Price**
orange            4
grapefruit        10
banana            15

我想写一个select语句，它会显示如下输出：

**Fruit**   **Price**
citrus      14
banana      15

还是SQL的新手，所以我无法弄清楚SELECT语句。如果这是SELECT语句，它将给我上面的第一组结果（逐项水果），我怎么能改变它以便它结合橙子和葡萄柚并将结果显示为柑橘？

SELECT
INV.fruit,
INV.price
FROM
INVENTORY      INV

Answer 1

您可以使用case声明：

select (case when fruit in ('orange', 'grapefruit') then citrus else fruit end) as fruit,
       sum(price) as price
from inventory i
group by (case when fruit in ('orange', 'grapefruit') then citrus else fruit end);

Answer 2

您可以使用case表达式将橙子和葡萄柚翻译成柑橘：

SELECT   CASE WHEN fruit IN ('orange', 'grapefruit')
              THEN 'citrus' 
              ELSE fruit 
         END,
         SUM(price)
FROM     inventory
GROUP BY CASE WHEN fruit IN ('orange', 'grapefruit')
              THEN 'citrus' 
              ELSE fruit 
         END

Answer 3

如果citrus是您需要多次使用的情况，请使用WITH子句，也称为subquery factoring。

WITH data AS( SELECT (case when fruit in ('orange', 'grapefruit') then citrus else fruit end)) as fruit, sum(price) as price from inventory i group by (case when fruit in ('orange', 'grapefruit') then citrus else fruit end) )......

对于更多此类情况，只需在WITH子句中包含子查询即可。最后，从中选择你想要的任何东西。

例如， WITH citrus as...., bitter as...etc.

SQL将2个不同的行合并为1

3 个答案: