編寫SQL案例並計數每一行

Question

我如何在下面獲得所需的結果？ 我可以通過添加DISTINCT來獲得所有唯一類別，但是在檢索每個類別的總數時 ，下面的查詢不起作用。

表結構：啤酒

ID | NAME | TYPE | ALCOHOL | 

所需結果

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

我的SQL查詢：

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;

有人可以引導我朝正確的方向前進嗎？

Answer 1

您需要一個count()和一個group by 。 我曾經使用CTE來避免殘酷的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

添加計數並按以下方式分組：

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

子查詢用於簡化GROUP BY ，因為Oracle不支持GROUP BY 1語法。

還要注意CASE更簡單的ELSE

Answer 3

您可以在CASE應用GROUP BY並找到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

使用條件相同的聚集函數以及group by

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