因需要在三个表中查东西，还不能要交集，要并集。
创建三张表
我用的是DBaver来创建，下面就是代码，跑完之后会出现三个表。
create table tas_master.hk_test_1(
id INT not null,
name1 varchar(100) NULL
);
create table tas_master.hk_test_2(
id INT not null,
name1 varchar(100) null,
name2 varchar(100) NULL
);
create table tas_master.hk_test_3(
id INT not null,
name1 varchar(100) null,
name3 varchar(100) NULL
);
insert into tas_master.hk_test_1
(id, name1)
values
(1, 's1'),
(2, 's2'),
(3, 's3');
insert into tas_master.hk_test_2
(id, name1, name2)
values
(2, 's2', '2s2'),
(3, 's3', '3s3'),
(4, 's4', '4s4');
insert into tas_master.hk_test_3
(id, name1, name3)
values
(1, 's1', '1l1'),
(1, 'ss1', '1l1'),
(2, 's2', '2l2'),
(3, 's3', '3l3'),
(4, 's4', '4l4'),
(5, 's5', '5l5');
select * from tas_master.hk_test_1;
select * from tas_master.hk_test_2;
select * from tas_master.hk_test_3;
第一个表tas_master.hk_test_1
| id | name1 |
|---|---|
| 2 | s2 |
| 3 | s3 |
| 1 | s1 |
第二个表tas_master.hk_test_2
| id | name1 | name2 |
|---|---|---|
| 2 | s2 | 2s2 |
| 3 | s3 | 3s3 |
| 4 | s4 | 4s4 |
第三个表tas_master.hk_test_3
| id | name1 | name3 |
|---|---|---|
| 3 | s3 | 3l3 |
| 2 | s2 | 2l2 |
| 5 | s5 | 5l5 |
| 1 | s1 | 1l1 |
| 1 | ss1 | 1l1 |
| 4 | s4 | 4l4 |
来三表联查一下吧
就是选用三个表的数据，一定是满足on条件的。
inner join 内连接
select coalesce(t1.id, t2.id, t3.id) as id, t1.name1, t2.name1, t2.name2, t3.name1, t3.name3 from
(select * from tas_master.hk_test_1) as t1
join (select * from tas_master.hk_test_2) as t2
on (t1.id = t2.id and t1.name1 = t2.name1)
join (select * from tas_master.hk_test_3) as t3
on (t2.id = t3.id and t3.name1 = t2.name1);
结果，可看作交集
| id | name1 | name1 | name2 | name1 | name3 |
|---|---|---|---|---|---|
| 3 | s3 | s3 | 3s3 | s3 | 3l3 |
| 2 | s2 | s2 | 2s2 | s2 | 2l2 |
full join 全连接
select coalesce(t1.id, t2.id, t3.id) as id, t1.name1, t2.name1, t2.name2, t3.name1, t3.name3 from
(select * from tas_master.hk_test_1) as t1
full join (select * from tas_master.hk_test_2) as t2
on (t1.id = t2.id)
full join (select * from tas_master.hk_test_3) as t3
on (t1.id = t3.id);
结果，可看作并集，注意on后面只能跟一个条件，多了不好用
| id | name1 | name1 | name2 | name1 | name3 |
|---|---|---|---|---|---|
| 2 | s2 | s2 | 2s2 | s2 | 2l2 |
| 1 | s1 | ss1 | 1l1 | ||
| 1 | s1 | s1 | 1l1 | ||
| 5 | s5 | 5l5 | |||
| 4 | s4 | 4s4 | |||
| 4 | s4 | 4l4 | |||
| 3 | s3 | s3 | 3s3 | s3 | 3l3 |
我们看下用不同的on后面条件，出来结果是否一样。
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insert into tas_master.hk_test_3
(id, name1, name3)
values
(6, 's1', '1l2');
tas_master.hk_test_3 就变成这样，多了id_6
| id | name1 | name3 |
|---|---|---|
| 3 | s3 | 3l3 |
| 6 | s1 | 1l2 |
| 5 | s5 | 5l5 |
| 2 | s2 | 2l2 |
| 1 | s1 | 1l1 |
| 1 | ss1 | 1l1 |
| 4 | s4 | 4l4 |
name1条件
select coalesce(t1.id, t2.id, t3.id) as id, t1.name1, t2.name1, t2.name2, t3.name1, t3.name3 from
(select * from tas_master.hk_test_1) as t1
full join (select * from tas_master.hk_test_2) as t2
on (t1.name1 = t2.name1)
full join (select * from tas_master.hk_test_3) as t3
on (t1.name1 = t3.name1);
| id | name1 | name1 | name2 | name1 | name3 |
|---|---|---|---|---|---|
| 3 | s3 | s3 | 3s3 | s3 | 3l3 |
| 1 | ss1 | 1l1 | |||
| 1 | s1 | s1 | 1l2 | ||
| 1 | s1 | s1 | 1l1 | ||
| 5 | s5 | 5l5 | |||
| 4 | s4 | 4s4 | |||
| 4 | s4 | 4l4 | |||
| 2 | s2 | s2 | 2s2 | s2 | 2l2 |
id条件
select coalesce(t1.id, t2.id, t3.id) as id, t1.name1, t2.name1, t2.name2, t3.name1, t3.name3 from
(select * from tas_master.hk_test_1) as t1
full join (select * from tas_master.hk_test_2) as t2
on (t1.id = t2.id)
full join (select * from tas_master.hk_test_3) as t3
on (t1.id = t3.id);
| id | name1 | name1 | name2 | name1 | name3 |
|---|---|---|---|---|---|
| 6 | s1 | 1l2 | |||
| 4 | s4 | 4s4 | |||
| 4 | s4 | 4l4 | |||
| 3 | s3 | s3 | 3s3 | s3 | 3l3 |
| 2 | s2 | s2 | 2s2 | s2 | 2l2 |
| 5 | s5 | 5l5 | |||
| 1 | s1 | ss1 | 1l1 | ||
| 1 | s1 | s1 | 1l1 |
两个还不是一样的，我认为只要on条件中，筛出来的那一列肯定是有值的。
我有尝试了不同的条件组合，发现这个on条件中还是只放一个为好，下面是我做的记录。
select t1.id, t2.id, t3.id, t1.name1, t2.name1, t2.name2, t3.name1, t3.name3 from
(select * from tas_master.hk_test_1) as t1
full join (select * from tas_master.hk_test_2) as t2
on (t1.id = t2.id)
full join (select * from tas_master.hk_test_3) as t3
on (t2.id = t3.id and t1.id = t3.id and t1.id = t2.id);
| id | id | id | name1 | name1 | name2 | name1 | name3 |
|---|---|---|---|---|---|---|---|
| 3 | 3 | 3 | s3 | s3 | 3s3 | s3 | 3l3 |
| 6 | s1 | 1l2 | |||||
| 1 | s1 | ||||||
| 1 | ss1 | 1l1 | |||||
| 1 | s1 | 1l1 | |||||
| 2 | 2 | 2 | s2 | s2 | 2s2 | s2 | 2l2 |
| 4 | s4 | 4s4 | |||||
| 4 | s4 | 4l4 | |||||
| 5 | s5 | 5l5 |
select t1.id, t2.id, t3.id, t1.name1, t2.name1, t2.name2, t3.name1, t3.name3 from
(select * from tas_master.hk_test_1) as t1
full join (select * from tas_master.hk_test_2) as t2
on (t1.id = t2.id)
full join (select * from tas_master.hk_test_3) as t3
on (t2.id = t3.id and t1.id = t3.id);
| id | id | id | name1 | name1 | name2 | name1 | name3 |
|---|---|---|---|---|---|---|---|
| 3 | 3 | 3 | s3 | s3 | 3s3 | s3 | 3l3 |
| 1 | s1 | ||||||
| 1 | ss1 | 1l1 | |||||
| 1 | s1 | 1l1 | |||||
| 6 | s1 | 1l2 | |||||
| 5 | s5 | 5l5 | |||||
| 2 | 2 | 2 | s2 | s2 | 2s2 | s2 | 2l2 |
| 4 | s4 | 4s4 | |||||
| 4 | s4 | 4l4 |
select t1.id, t2.id, t3.id, t1.name1, t2.name1, t2.name2, t3.name1, t3.name3 from
(select * from tas_master.hk_test_1) as t1
full join (select * from tas_master.hk_test_2) as t2
on (t1.id = t2.id)
full join (select * from tas_master.hk_test_3) as t3
on (t2.id = t3.id);
| id | id | id | name1 | name1 | name2 | name1 | name3 |
|---|---|---|---|---|---|---|---|
| 3 | 3 | 3 | s3 | s3 | 3s3 | s3 | 3l3 |
| 5 | s5 | 5l5 | |||||
| 4 | 4 | s4 | 4s4 | s4 | 4l4 | ||
| 2 | 2 | 2 | s2 | s2 | 2s2 | s2 | 2l2 |
| 1 | s1 | ||||||
| 1 | ss1 | 1l1 | |||||
| 1 | s1 | 1l1 | |||||
| 6 | s1 | 1l2 |
left join 左连接
这个就简单了就是以左边的为准。
select t1.id, t2.id, t3.id, t1.name1, t2.name1, t2.name2, t3.name1, t3.name3 from
(select * from tas_master.hk_test_1) as t1
left join (select * from tas_master.hk_test_2) as t2
on (t1.id = t2.id)
left join (select * from tas_master.hk_test_3) as t3
on (t1.id = t3.id);
| id | id | id | name1 | name1 | name2 | name1 | name3 |
|---|---|---|---|---|---|---|---|
| 1 | 1 | s1 | ss1 | 1l1 | |||
| 1 | 1 | s1 | s1 | 1l1 | |||
| 3 | 3 | 3 | s3 | s3 | 3s3 | s3 | 3l3 |
| 2 | 2 | 2 | s2 | s2 | 2s2 | s2 | 2l2 |
select t1.id, t2.id, t3.id, t1.name1, t2.name1, t2.name2, t3.name1, t3.name3 from
(select * from tas_master.hk_test_1) as t1
left join (select * from tas_master.hk_test_2) as t2
on (t1.id = t2.id)
left join (select * from tas_master.hk_test_3) as t3
on (t3.id = t2.id);
| id | id | id | name1 | name1 | name2 | name1 | name3 |
|---|---|---|---|---|---|---|---|
| 1 | s1 | ||||||
| 3 | 3 | 3 | s3 | s3 | 3s3 | s3 | 3l3 |
| 2 | 2 | 2 | s2 | s2 | 2s2 | s2 | 2l2 |
给我的感觉是，三表联查，主要是看on条件中是什么样的。想三表联查还是with写好点。