mysql连表

Question

A 表
user_id    phone
  1                1
  2                2

B表
user_id    mail
  1             1

想连表得到C，没有找到相同user_id的默认为0

C表
user_id   phone   mail
  1              1          1
  2              2          0

mysql语句怎么写？

Answer 1

select A.user_id as user_id,A.phone as phone,coalesce(B.mail,0) as mail
from A left join B on A.user_id=B.user_id