Question

mysql对多表关联出来的数据如何去重？

table1:
id name mobile
1 Gosh 11111111
2 Sansy 22222222
3 Join 33333333

table2:
id city table1_id wife
1 beijing 3 a
2 beijing 3 b
3 xian 1 c
4 xian 1 d
5 shandong 2 e
6 shandong 2 f

关联这两张表，得到id,name,mobile,city：
select id,name,mobile,city from table1 left join table2 on table1.id = table2.table1_id;
结果:
id name mobile city
1 Gosh 11111111 xian
1 Gosh 11111111 xian
2 Sansy 22222222 shandong
2 Sansy 22222222 shandong
3 Join 33333333 beijing
3 Join 33333333 beijing

怎样写SQL让得出来的重复数据只保留一条有用信息呢？
其实只要最后group by id,name,mobile,city即可，group by有时候也可以起到去重的效果

Answer 1

select distinct id,name,mobile,city from table1 left join table2 on table1.id = table2.table1_id;