SQL JOINS 七种理论模型
1.左外连接(左表独有+右表共有)
select <select list> from tableA A left join tableB B on A.key=B.key
2.右外连接(右表独有+左表共有)
select <select list> from tableA A right join tableB B on A.key=B.key
3.内连接(左表+右表共有)
select <select list> from tableA A inner join tableB B on A.key=B.key
4.左连接(左表独有)
select <select list> from tableA A left join tableB B on A.key=B.key where B.key is null
5.右连接(右表独有)
select <select list> from tableA A left join tableB B on A.key=B.key where A.key is null
6.全连接(左表全表+右表全表)
MySQL写法:select <select list> from tableA A left join tableB B on A.key=B.key union select <select list> from tableA A right join tableB B on A.key=B.key
Oracle写法select <select list> from tableA A full outer join tableB B on.key=B.key
7.独连接(左表独有或右表独有)
MySQL写法select <select list> from tableA A left join tableB B on A.key=B.key where A.key is null union select <select list> from tableA A right join tableB B on A.key=B.key where B.key is null
Oracle写法select <select list> from tableA A full outer tableB B A.key=B.key where A.key is null or B.key is null