left join(左联接) 返回包括左表中的所有记录和右表中联结字段相等的记录。
select * from app01_publisher left join app01_book on app01_publisher.id = app01_book.publish_id
right join(右联接) 返回包括右表中的所有记录和左表中联结字段相等的记录。
select * from app01_publisher right join app01_book on app01_publisher.id = app01_book.publish_id
inner join(等值连接) 只返回两个表中联结字段相等的行。
select * from app01_publisher inner join app01_book on app01_publisher.id = app01_book.publish_id