sql test

1、用户表

找出id=2及他的朋友

select * from user t where id=2 or t.id=(select friend from user where id=2);

select * from user t where id=2 union select * from user where id in(select friend from user where id=2)

2、用户表

设备表

将拥有相同的公司的设备id填入到用户表中

update user2 t1 set device=(select d_id from device t2 where t1.company=t2.company);

update user2,device set user2.device=device.d_id where user2.company=device.comany;