Sql 使用Group By时计算多个值

如果这个问题含糊不清，我很抱歉，我是SQL新手，遇到了一些问题。我试图找出每个体重组的人数。计算该数字并显示每个类的数量

我认为我的问题在于当时的表达方式。我是否需要为每个体重组创建一个变量进行比较

多谢各位

SELECT 
(CASE WHEN pl_weight <180 THEN 1
WHEN pl_weight >=180 AND pl_weight <200 THEN 2
WHEN pl_weight >=200 AND pl_weight <220 THEN 3
ELSE 4 END),
count(1) "Less than 280", count(2)"180-200", count(3)"200-220",count(4)"More than 220"  
FROM dl_player
GROUP BY (CASE WHEN pl_weight <180 THEN 1
WHEN pl_weight >=180 AND pl_weight <200 THEN 2
WHEN pl_weight >=200 AND pl_weight <220 THEN 3
ELSE 4
END));

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一种方法是使用如下条件聚合：

SELECT 
    SUM(CASE WHEN "pl_weight" <180 THEN 1 ELSE 0 END) AS "Less than 280",
    SUM(CASE WHEN "pl_weight" >=180 AND "pl_weight" <200 THEN 1 ELSE 0 END) AS "180-200",
    SUM(CASE WHEN "pl_weight" >=200 AND "pl_weight" <220 THEN 1 ELSE 0 END) AS "200-220",
    SUM(CASE WHEN "pl_weight" >=220 THEN 1 ELSE 0 END) AS "More than 220"  
FROM dl_player

计数没有按你所希望的方式工作；它统计行数，或者更具体地说，统计其中的值不为NULL的行数。您可以使用条件聚合（如@jpw的答案中所示）完成此操作，也可以使用子查询完成此操作：

SELECT weight, COUNT(*) FROM (
    SELECT CASE WHEN pl_weight <180 THEN "Less than 180"
        WHEN pl_weight >=180 AND pl_weight <200 THEN "180-200"
        WHEN pl_weight >=200 AND pl_weight <220 THEN "200-220"
        ELSE "More than 220" END AS weight
      FROM dl_player
) GROUP BY weight;

---

顺便说一句，我不确定你是否注意到了，但在你的最后一个案例中，你有一个一个接一个的错误。如果值大于等于220，则返回4或大于220。

谢谢，这很有帮助。我想你必须使用组，所以这是造成我的问题。@ USSR248621如果我的答案有助于解决您的问题，请考虑将其标记为接受。

SELECT weight, COUNT(*) FROM (
    SELECT CASE WHEN pl_weight <180 THEN "Less than 180"
        WHEN pl_weight >=180 AND pl_weight <200 THEN "180-200"
        WHEN pl_weight >=200 AND pl_weight <220 THEN "200-220"
        ELSE "More than 220" END AS weight
      FROM dl_player
) GROUP BY weight;