sql - SQL查询（分组）按列的条件

Question

如果我想进行查询以获取分组年龄的用户计数

每年单独计算：

select count(*) 
from tbl_user 
group by age 

如何创建自定义组，以便我可以获取范围内的年龄，例如......就像这个例子：

group by ages as 0-18 , 19-25 , 26-...

Answer 1

在子查询中使用CASE表达式并在外部查询中按该表达式分组：

select age_group, count(*) 
from (
  select case when age between  0 and 18 then '0-18'
              when age between 19 and 26 then '19-25'
              ...
              end as age_group
  from tbl_user
) t
group by age_group

Answer 2

SUM 1 和 CASE WHEN 在 MS SQL Server 中工作时，您使用的是哪个版本的 SQL？

SELECT
    SUM(CASE WHEN Age >= 0 AND Age <= 18 THEN 1 ELSE 0 END) AS [0-18],
    SUM(CASE WHEN Age >= 19 AND Age <= 25 THEN 1 ELSE 0 END) AS [19-25]
FROM
    YourTable

Answer 3

您可以使用以下CASE语句：

SELECT Sum(CASE WHEN age BETWEEN 0 AND 18 THEN 1 ELSE 0 END) as [0-18],
Sum(CASE WHEN age BETWEEN 19 AND 25 THEN 1 ELSE 0 END) as [19-25],
Sum(CASE WHEN age BETWEEN 26 AND 34 THEN 1 ELSE 0 END) as [26-34]
FROM tbl_user

这会将数据“展平”为一行 - 要为每个分组获取一行，请将此作为视图的基础，然后从中进行选择。

Answer 4

数据属于表格，而不是代码。年龄类别是数据，恕我直言。

CREATE TABLE one
        ( val SERIAL NOT NULL PRIMARY KEY
        , age INTEGER NOT NULL
        );
INSERT INTO one (age) SELECT generate_series(0,31, 1);

CREATE TABLE age_category
        ( low INTEGER NOT NULL PRIMARY KEY
        , high INTEGER NOT NULL
        , description varchar
        );
INSERT INTO age_category (low,high,description) VALUES
   ( 0,19, '0-18')
 , ( 19,26, '19-25')
 , ( 26,1111, '26-...')
        ;

SELECT ac.description, COUNT(*)
FROM one o
JOIN age_category ac ON o.age >= ac.low AND o.age < ac.high
GROUP BY ac.description
        ;