SQL中連接JOIN語句可以分爲:
1,內部連接inner join,僅返回表A和表B中連接列匹配的那些行:
select * from A inner join B on A.k=B.k;
2,外部連接outer join,返回表A和表B中連接列匹配和不匹配的那些行,還能返回表A和表B中連接列爲NULL的那些行:
select * from A outer join B on A.k=B.k;
3,左連接left join和右連接right join,都屬於外部連接類型,返回類型與外連接類似:
select * from A left join B on A.k=B.k;
select * from A right join B on A.k=B.k;