mysql - 在SQL中将多个查询组合成一个查询

Question

我在 sql 中遇到问题，因为我对此很陌生。

我有三个问题

select count(*) as range1_50to60 from Customers where age between 50 and 60;

select count(*) as range2_30to40 from Customers where age between 30 and 40;

select count(*) as range3_20to30 from Customers where age between 20 and 30;

有什么方法可以将这些查询组合成一个查询。

问候

萨米拉

Answer 1

使用case表达式做条件聚合:

select count(case when age between 50 and 60 then 1 end) as range1_50to60,
       count(case when age between 30 and 40 then 1 end) as range2_30to40,
       count(case when age between 20 and 30 then 1 end) as range3_20to30
from Customers

where age between 20 and 60

WHERE 子句并不是真正需要的，但可能会加快速度!