三张表方法1:(内连接)SELECT u.id,u.name,u.phone,c.name from A u,B i,C c where u.id = i.userid and c.id = b.campus方法2:(左连接)SELECT u.id,u.name,u.phone,c.name from user uleft join B i on u.id = i.userid left join C c on c.id = i.campus;