sql查询从3个表中分离值，基于一列值

Question

我有3个表，结果表应该有所有三个表中的列基于第一个表的列user_id。

Answer 1

假设10，约翰应为15，约翰这看起来像一个非常简单的加入。如果以下型号不正确，请复制，编辑并添加到您的问题。

drop table if exists t1,t2,t3; 

create table t1(u_id int, name varchar(10), prd int); 
create table t2(u_id int, temp int); 
create table t3(u_id int, Office int); 

insert into t1 values (10,'ram',1), (15,'john',1),(20,'sat',1),(12,'peter',1); 
insert into t2 values (10,32),(20,42),(15,25),(12,32); 
insert into t3 values (20,56),(10,57),(15,56),(12,57); 

这个查询

select t1.*,t2.*,t3.* 
from t1 
join t2 on t2.u_id = t1.u_id 
join t3 on t3.U_id = t1.u_id 
order by t1.u_id; 

产生以下结果

+------+-------+------+------+------+------+--------+ 
| u_id | name | prd | u_id | temp | u_id | Office | 
+------+-------+------+------+------+------+--------+ 
| 10 | ram | 1 | 10 | 32 | 10 |  57 | 
| 12 | peter | 1 | 12 | 32 | 12 |  57 | 
| 15 | john | 1 | 15 | 25 | 15 |  56 | 
| 20 | sat | 1 | 20 | 42 | 20 |  56 | 
+------+-------+------+------+------+------+--------+ 
4 rows in set (0.00 sec) 

如果模型看起来像这样

drop table if exists t1,t2,t3; 

create table t1(u_id int, name varchar(10), prd int); 
create table t2(u_id int, temp int); 
create table t3(u_id int, Office int); 

insert into t1 values (10,'ram',1), (15,'john',1),(20,'sat',1),(12,'peter',1); 
insert into t2 values (10,32),(20,42),(10,25),(12,32); 
insert into t3 values (20,56),(10,57),(10,60),(10,56),(12,57); 

您可能需要模拟一个完整的加盟

select t1.u_id,t1.name,t2temp,t3office 
from t1 
join 
(
select t2.u_id as t2id, t2.temp as t2temp, t3.u_id as t3uid,t3.office as t3office 
from 
(
select t2.*,if(t2.u_id <> @p ,@rn:=1,@rn:=@rn+1) rn,@p:=t2.u_id from t2 ,(select @rn:=0,@p:=0) rn order by t2.u_id 
) t2 
left outer join 
(
select t3.*,if(t3.u_id <> @p1 ,@rn1:=1,@rn1:=@rn1+1) rn,@p1:=t3.u_id from t3 ,(select @rn1:=0,@p1:=0) rn1 order by t3.u_id 
) t3 on t3.u_id = t2.u_id and t2.rn = t3.rn 
union all 
select t2.u_id as t2id, t2.temp as t2temp, t3.u_id as t3uid,t3.office as t3office 
from 
(
select t2.*,if(t2.u_id <> @p ,@rn:=1,@rn:=@rn+1) rn,@p:=t2.u_id from t2 ,(select @rn:=0,@p:=0) rn order by t2.u_id 
) t2 
right outer join 
(
select t3.*,if(t3.u_id <> @p1 ,@rn1:=1,@rn1:=@rn1+1) rn,@p1:=t3.u_id from t3 ,(select @rn1:=0,@p1:=0) rn1 order by t3.u_id 
) t3 on t3.u_id = t2.u_id and t2.rn = t3.rn 
where t2.rn is null 
) z on t1.u_id = t2id or t1.u_id = t3uid 
order by t1.u_id  

+------+-------+--------+----------+ 
| u_id | name | t2temp | t3office | 
+------+-------+--------+----------+ 
| 10 | ram | NULL |  56 | 
| 10 | ram |  32 |  57 | 
| 10 | ram |  25 |  60 | 
| 12 | peter |  32 |  57 | 
| 20 | sat |  42 |  56 | 
+------+-------+--------+----------+ 
5 rows in set (0.00 sec)