Sql查询根据一个列值从3个表中隔离值

Question

我有3个表，结果表应该包含来自所有三个表的列，这些列基于第一个表的列cc_library.srcs。

Answer 1

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

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);

此查询

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;

产生此结果

+------+-------+------+------+------+------+--------+
| 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);

您可能需要模拟完整联接

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)