链接查询
join
链接语句, 将很多条语句合并成一个语句, (相比于双重循环)大大减少了通过网络传输的次数.
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select account ,user.name as username , role.name as rolename
from auth_user user
INNER JOIN auth_user_role ur
on ur.user_id = user.id
INNER JOIN auth_role role
on ur.role_id=role_id
