使用 union all 和 union

1.新建兩張表：student、teacher
//學生表
create table student(
id int primary key,
name varchar(40)
);
//老師表
create table teacher(
id int primary key,
name varchar(40)
);

2.分別給兩張表加入一條記錄
insert into student(id,name) values(1,'student1');
insert into teacher(id,name) values(2,'teacher1');

3.查詢并集：
方式一（不去重復）：
select * from student
union all
select * from teacher;

方式二（去掉重復）：
select * from student
union
select * from teacher;

帶where子句的：
select * from student
where id = 1
union all
select * from teacher;

加字段區(qū)分記錄是數(shù)據(jù)哪個表的:
select a.*, '1' as belongf from student a
union all
select b.*, '0' as belongf from teacher b;

加order by子句：
select * from
(
select a.*, '1' as belongf from student a
union all
select b.*, '0' as belongf from teacher b
) t
order by belongf desc,id desc;

查并集的總記錄數(shù)：
select count(1) as mycount from (
select a.*, '1' as belongf from student a
union all
select b.*, '0' as belongf from teacher b
) d;

?

轉(zhuǎn)載于:https://www.cnblogs.com/chentu279203653/p/9450143.html

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