Sql Jions 的简易理解
Select * from TableA A left jion TableB B on A.key = B.key
Select * from TableA A right jion TableB B on A.key = B.key
Select * from TableA A inner jion TableB B on A.key = B.key
Select * from TableA A left jion TableB B on A.key = B.key where B.key is NULL
Select * from TableA A right jion TableB B on A.key = B.key where A.key is NULL
Select * from TableA A full outer jion TableB B on A.key = B.key
Select * from TableA A full outer jion TableB B on A.key = B.key where A.key is NULL or B.key is NULL