SQL中JOIN的使用
(注:outer的意思就是"没有关联上的行"。)
1.cross join 全外连接(笛卡尔乘积)
SELECT A.*, B.* from A FULL OUTER JOIN B ON A.ID = B.ID
2.inner join 内连接(在笛卡尔乘积的结果集中去掉不符合连接条件的行)
SELECT A.* from A INNER JOIN B ON A.ID=B.ID
3.left outer join 左外连接(在inner join的结果集上加上左表中没被选上的行，行的右表部分每个字段都用NUll填充)
SELECT A.* from A LEFT JOIN B ON A.ID = B.ID
4.right outer join 右外连接(在inner join的结果集上加上右表中没被选上的行，行的左表部分全用NULL填充。)
SELECT A.* from A RIGHT JOIN B ON A.ID = B.ID
举例说明：
表A
记录如下：
aID aNum
1 a20050111
2 a20050112
3 a20050113
4 a20050114
5 a20050115
表B
记录如下:
bID bName
1 2006032401
2 2006032402
3 2006032403
4 2006032404
8 2006032408
实验如下
:
1.left join
sql
语
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