三个表和成一张表 ~
table   1
id   name   sex
1       aaa     s
2       aaa2     s2
table   2
id       table1_id     adress
1             1                       ss
2             2                       ss2
table   3
id   table1_id       old
1               1               12
例如想这样的表   第三个表只有其中的几个字段     合并为
table   4
id       name     sex   adress   old
1           aaa         s       ss           12
2           aaa2       s2     ss2           null

------解决方案--------------------
select a.*,b.adress,c.old from table1 a left join table2 b on a.id=b.id left join table3 c on a.id=c.id
------解决方案--------------------
table 1
id name sex
1 aaa s
2 aaa2 s2
table 2
id table1_id adress
1 1 ss
2 2 ss2
table 3
id table1_id old
1 1 12
------------------
select a.*,b.adress,c.old
from t1 a left join t2 b on a.id=b.table1_id
left join t3 c on a.id=c.table1_id


------解决方案--------------------
select table1.id,name,sex,adress,old from table1 left join table2 on table1.id = table2.table1_id left join table3 on table1.id = table3.table1_id
------解决方案--------------------
select a.*,b.adress,c.old from [table_1] a left join [table_2] b on a.id=b.table1_id left join [table_3] c on a.id=c.table1_id
------解决方案--------------------
create table table1(id int,name varchar(10),sex varchar(10))
insert table1
select 1 , 'aaa ', 's '
union select 2 , 'aaa2 ', 's2 '
create table table2(id int,table1_id int,adress varchar(10))
insert table2
select 1 ,1, 'ss '
union select 2,2, 'ss2 '
create table table3(id int,table1_id int,old int)
insert table3
select 1 , 1 , 12


select a.*,b.adress,c.old from table1 a left join table2 b on a.id=b.table1_id left join table3 c on a.id=c.table1_id

drop table table1,table2,table3
------解决方案--------------------
select a.*,b.adress,c.old
from table1 a left join table2 b on a.id=b.table1_id
left join table3 c on a.id=c.table1_id