mysql联合查询问题

[amu1433]

Persons" 表：
Id_P LastName FirstName Address City
1 Adams John Oxford Street London
2 Bush George Fifth Avenue New York
3 Carter homas Changan Street Beijing


"Orders" 表：
Id_O OrderNo Id_P
1 77895 3
2 44678 3
3 22456 1
4 24562 1
5 34764 65


怎么查询Persons表id=1 对应Orders的数量

就是
Id_P(1) Adams 2
Id_P(2) Bush 0
Id_P(3) Carter 2

[暖冬_WarmWinter]

比较建议在用户表增加一个字段做统计

[TechSas]

select Id_P(1) ,LastName from Persons,Orders where Id_O=Id_P;

[TechSas]

select Id_P ,LastName from Persons,Orders where Id_O=Id_P;

[TechSas]

order应该新建一张表，字段有id_order和orders，然后让子表的主键=主表的子键，然后在进行联表查询 这样比较好，我上边写的是查询了你需要查询的某些字段，剩下的order的数量你用我这个方法试着写就行

[一起混吧]

select p.Id_P ,p.LastName,(select count(*) from Orders where Id_P=p.Id_P) as counter from Persons p

[misaka去年夏天]

select count(Id_P) as shuliang from Orders where Orders.Id_P in (select Id_P from Persons) group by Id_P;