SQL JOINS

①左外连接

select field from TableA A left join TableB B on A.key = B.key

②左外连接，去掉右侧键值

select field from TableA A left join TableB B on A.key = B.key
where B.key IS NULL

③内连接，

select field from TableA A inner join Table B on A.key = B.key

④右外连接

select field from TableA A right join Table B on A.key = B.key

⑤右外连接，去掉左侧键值

select field from TableA A right join TableB B on A.key = B.key
where A.key IS NULL

⑥全连接

select field from TableA A full outer join TableB B on A.key = B.key

⑦全连接，去掉左右键值

select field from TableA A full outer join TableB B on A.key = B.key