在 SQL 中将多个查询组合成一个查询

Question

我在 sql 中遇到了一个问题，因为我对此很陌生。

我有三个查询

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表达式进行条件聚合：

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，但可以加快速度！

Answer 2

你可以像这样使用SUM：

SELECT SUM(IF(age between 50 and 60,1,0)) AS range1_50to60, 
       SUM(IF(age between 30 and 40,1,0)) AS range1_30to40, 
       SUM(IF(age between 20 and 30,1,0)) AS range1_20to30 
FROM Customers

Answer 3

您可以尝试使用 UNION ALL 连接所有查询，它会像这样结束。

select count(*) as result from Customers where age between 50 and 60
union all
select count(*) as result from Customers where age between 30 and 40;
union all
select count(*) as result from Customers where age between 20 and 30;

结果将是：

row[0] for range1_50to60
row[1] for range2_30to40 
row[2] for range3_20to30

Answer 4

首先我们有我们的虚拟数据

CREATE TABLE persons(
    person_id NUMBER GENERATED BY DEFAULT AS IDENTITY,
    first_name VARCHAR2(50) NOT NULL,
    last_name VARCHAR2(50) NOT NULL,
    age NUMBER,
    PRIMARY KEY(person_id)
);
insert all 
    into persons(person_id,first_name,last_name,age) values(1,'jose','alvarez',32)
    into persons(person_id,first_name,last_name,age) values(2,'karla','romagnoli',24)
    into persons(person_id,first_name,last_name,age) values(3,'daniela','alcazar',24)
    into persons(person_id,first_name,last_name,age) values(4,'jaime','camilo',44)
    into persons(person_id,first_name,last_name,age) values(5,'jenifer','paola',22)
    into persons(person_id,first_name,last_name,age) values(6,'camila','puertas',55)
    into persons(person_id,first_name,last_name,age) values(7,'raul','duelas',30)
    into persons(person_id,first_name,last_name,age) values(8,'alejandra','bautizal',60)
    into persons(person_id,first_name,last_name,age) values(9,'domingo','cano',16)
    into persons(person_id,first_name,last_name,age) values(10,'felipe','vaca',25)
    into persons(person_id,first_name,last_name,age) values(11,'estefany','santes',28)
    into persons(person_id,first_name,last_name,age) values(12,'pamela','chu',55)
    into persons(person_id,first_name,last_name,age) values(13,'fernanda','zarate',67)
select 1 from dual;

由于您只需要一行数据，再加上这些最终结果彼此不相关这一事实，我们可以通过这种方式将它们与笛卡尔积集成：

select 
q1.total as age20_30,
q2.total as age31_40,
q3.total as age50_60
from (
    select count(*) as total from persons p
    where p.age between 20 and 30
) q1, (
    select count(*) as total from persons p
    where p.age between 31 and 40
) q2, (
    select count(*) as total from persons p
    where p.age between 50 and 60
) q3 ;

我们得到下一个结果

age20_30	age31_40	age50_60
6	1	3