编写SQL案例并计数每一行

Question

我如何在下面获得所需的结果？ 我可以通过添加DISTINCT来获得所有唯一类别，但是在检索每个类别的总数时 ，下面的查询不起作用。

表结构：啤酒

ID | NAME | TYPE | ALCOHOL | 

所需结果

category   |  total
----------------------------
Light      | 34
Medium     | 2
Normal     | 3
Heavy      | 4
Knock out  | 5

我的SQL查询：

SELECT 
   CASE WHEN b.ALCOHOL < 3 THEN 'Light'
        WHEN b.ALCOHOL < 5 THEN 'Medium'
        WHEN b.ALCOHOL < 7 THEN 'Normal'
        WHEN b.ALCOHOL < 9 THEN 'Heavy'
        WHEN b.ALCOHOL >= 9 THEN 'Knock out'
   END AS category
FROM BEER b;

有人可以引导我朝正确的方向前进吗？

Answer 1

您需要一个count()和一个group by 。 我曾经使用CTE来避免残酷的group by

with CTE as
(
SELECT 
   CASE WHEN b.ALCOHOL < 3 THEN 'Light'
            WHEN b.ALCOHOL < 5 THEN 'Medium'
                WHEN b.ALCOHOL < 7 THEN 'Normal'
                WHEN b.ALCOHOL < 9 THEN 'Heavy'
                WHEN b.ALCOHOL >= 9 THEN 'Knock out'
   END AS category,
   b.Alcohol
     FROM BEER b
)
select category, count(alcohol)
from CTE
group by category

Answer 2

添加计数并按以下方式分组：

SELECT Category, COUNT(*) AS Total FROM (
  SELECT 
    CASE WHEN b.ALCOHOL < 3 THEN 'Light'
         WHEN b.ALCOHOL < 5 THEN 'Medium'
         WHEN b.ALCOHOL < 7 THEN 'Normal'
         WHEN b.ALCOHOL < 9 THEN 'Heavy'
         ELSE 'Knock out'
    END AS Category
  FROM BEER) b
GROUP BY Category

子查询用于简化GROUP BY ，因为Oracle不支持GROUP BY 1语法。

还要注意CASE更简单的ELSE

Answer 3

您可以在CASE应用GROUP BY并找到COUNT

SELECT 
   CASE WHEN b.ALCOHOL < 3 THEN 'Light'
        WHEN b.ALCOHOL < 5 THEN 'Medium'
        WHEN b.ALCOHOL < 7 THEN 'Normal'
        WHEN b.ALCOHOL < 9 THEN 'Heavy'
        WHEN b.ALCOHOL >= 9 THEN 'Knock out'
   END AS category,
   count(*) total
FROM BEER b
GROUP BY 
    CASE WHEN b.ALCOHOL < 3 THEN 'Light'
        WHEN b.ALCOHOL < 5 THEN 'Medium'
        WHEN b.ALCOHOL < 7 THEN 'Normal'
        WHEN b.ALCOHOL < 9 THEN 'Heavy'
        WHEN b.ALCOHOL >= 9 THEN 'Knock out'
   END;

Answer 4

使用条件相同的聚集函数以及group by

sum(CASE WHEN b.ALCOHOL < 3 THEN 1 else 0 end)
....
from tbl1
group by some_col