两个SELECT语句之间的MySQL笛卡尔积

Question

我想在两个SELECT语句之间执行笛卡尔积

SELECT 1, 2     INNER JOIN     SELECT 3, 4 ;

我希望结果是(1,2)和(3,4)的每个组合,如:

1  3
2  3
1  4
2  4

Answer 1

如果您在表中指定了没有任何JOIN ON条款或等式/条件的表格,WHERE您将获得您正在寻找的catesian产品.

SELECT table1.field1, table2.field2
FROM table1, table2

会给你你所要求的.更明确地展示它......

SELECT * FROM table1;
+--------+
| field1 |
+--------+
|      1 |
|      2 |
+--------+

SELECT * FROM table2;
+--------+
| field2 |
+--------+
|      3 |
|      4 |
+--------+

SELECT table1.field1, table2.field2 FROM table1, table2;
+--------+--------+
| field1 | field2 |
+--------+--------+
|      1 |      3 |
|      2 |      3 |
|      1 |      4 |
|      2 |      4 |
+--------+--------+

Answer 2

您可以使用CROSS JOIN子句

SELECT MyTable1.Col1, MyTable2.Col2
FROM MyTable1
CROSS JOIN MyTable2

其中MyTable1有两行,包含1和2; 和MyTable2有两行包含3和4.