记录一次业务解决两个表之间的逻辑涉及的sql

1、两个表之间sql逻辑left join,right join,inner join,full join之间的区别:

感谢：https://www.cnblogs.com/lijingran/p/9001302.html

但是 

 SELECT p.LastName, p.FirstName, o.OrderNo
FROM Persons p
INNER JOIN Orders o
ON p.Id_P=o.Id_P and 1=1　　--用and连接多个条件
ORDER BY p.LastName

和SELECT p.LastName, p.FirstName, o.OrderNo
FROM Persons p，Orders o
where  p.Id_P=o.Id_P   的效果是一样的

2、A表中有个字段column_aa，B表中有个字段column_bb
如果需要查询出B表中字段column_bb like A表中column_aa字段的纪录，可以使用如下语句
select A.* from A left join B on column_aa like concat("%",column_bb,"%")  ;

感谢：https://www.cnblogs.com/kingxiaozi/p/6393168.html

3、【Mysql】求两个表（查询结果）的差集
select id from usertable   where id not in (select id from blog)

https://blog.csdn.net/yongh701/article/details/51689976

4、如何查询一个表中某个字段相同的数据，如下
select * from students group by teacher_id HAVING COUNT(teacher_id)>1;