SQL中如何查询A表全部数据与A表有关联的B表部分数据

1、创建测试表，

create table test_col_1(id number, var varchar2(200))

create table test_col_2(id number, var varchar2(200))

2、插入测试数据，

insert into test_col_1

select level*8, 'var'||level*8 from dual connect by level <= 20

insert into test_col_2

select level, 'var'||level from dual connect by level <= 100

3、查询A表与B表关联记录，

select *

from test_col_2 b

where exists (select 1 from test_col_1 a where b.id = a.id)

4、查询A表全部数据及A、B有关联的数据，

select *

from test_col_1 a

union all

select *

from test_col_2 b

where exists (select 1 from test_col_1 a where b.id = a.id)

left join 是左关联，就是以左边的表为主表，左边表的数据全部展示，右边的表只展示能关联到左边的表。你用inner join 试试

select * from a表 a inner join b表 b on b.activity_id=a.id

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