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计算两个相关联表的笛卡尔积(CROSS JOIN) ，生成虚拟表VT1-J1。
- mysql> select * from table1,table2;
- +-----+------+-----+------+
- | uid | name | oid | uid |
- +-----+------+-----+------+
- | aaa | mike | 1 | aaa |
- | bbb | jack | 1 | aaa |
- | ccc | mike | 1 | aaa |
- | ddd | mike | 1 | aaa |
- | aaa | mike | 2 | aaa |
- | bbb | jack | 2 | aaa |
- | ccc | mike | 2 | aaa |
- | ddd | mike | 2 | aaa |
- | aaa | mike | 3 | bbb |
- | bbb | jack | 3 | bbb |
- | ccc | mike | 3 | bbb |
- | ddd | mike | 3 | bbb |
- | aaa | mike | 4 | bbb |
- | bbb | jack | 4 | bbb |
- | ccc | mike | 4 | bbb |
- | ddd | mike | 4 | bbb |
- | aaa | mike | 5 | bbb |
- | bbb | jack | 5 | bbb |
- | ccc | mike | 5 | bbb |
- | ddd | mike | 5 | bbb |
- | aaa | mike | 6 | ccc |
- | bbb | jack | 6 | ccc |
- | ccc | mike | 6 | ccc |
- | ddd | mike | 6 | ccc |
- | aaa | mike | 7 | NULL |
- | bbb | jack | 7 | NULL |
- | ccc | mike | 7 | NULL |
- | ddd | mike | 7 | NULL |
- +-----+------+-----+------+
- 28 rows in set (0.00 sec)
2.2、(1-J2)ON过滤
基于虚拟表VT1-J1这一个虚拟表进行过滤，过滤出所有满足ON 谓词条件的列，生成虚拟表VT1-J2。
注意：这里因为语法限制，使用了'WHERE'代替，从中读者也可以感受到两者之间微妙的关系;
- mysql> SELECT
- -> *
- -> FROM
- -> table1,
- -> table2
- -> WHERE
- -> table1.uid = table2.uid
- -> ;
- +-----+------+-----+------+
- | uid | name | oid | uid |
- +-----+------+-----+------+
- | aaa | mike | 1 | aaa |
- | aaa | mike | 2 | aaa |
- | bbb | jack | 3 | bbb |
- | bbb | jack | 4 | bbb |
- | bbb | jack | 5 | bbb |
- | ccc | mike | 6 | ccc |
- +-----+------+-----+------+
- 6 rows in set (0.00 sec)
2.3、(1-J3)添加外部列 （编辑：晋中站长网）
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