两个 SELECT 语句之间的 MySQL 笛卡尔积
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MySQL cartesian product between two SELECT statements
提问by bobobobo
I want to perform a cartesian product between two SELECT statements as
我想在两个 SELECT 语句之间执行笛卡尔积作为
SELECT 1, 2 INNER JOIN SELECT 3, 4 ;
I expect the result to be every combination of (1,2) with (3,4), like:
我希望结果是 (1,2) 和 (3,4) 的每个组合，例如：
1 3
2 3
1 4
2 4
回答by Riedsio
If you specify your tables with out any JOIN ONclause or equalities/conditionins in the WHEREclause you'll get the catesian product you're looking for.
如果您在JOIN ON子句中指定没有任何子句或等式/条件的表，WHERE您将获得您正在寻找的 catesian 产品。
SELECT table1.field1, table2.field2
FROM table1, table2
will give you what you're asking for. Showing it more explicitly...
会给你你所要求的。更明确地显示它...
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 |
+--------+--------+
回答by bobs
You can use the CROSS JOIN clause
您可以使用 CROSS JOIN 子句
SELECT MyTable1.Col1, MyTable2.Col2
FROM MyTable1
CROSS JOIN MyTable2
where MyTable1 has two rows containing 1 and 2; and MyTable2 has two rows containing 3 and 4.
其中 MyTable1 有两行包含 1 和 2；MyTable2 有两行包含 3 和 4。
回答by Athari
select v1, v2
from
(select 1 as v1 union
select 2) t1,
(select 3 as v2 union
select 4) t2
or even simpler:
甚至更简单：
select *
from
(select 1 union
select 2) t1,
(select 3 union
select 4) t2
回答by Ashish Kumar
With the using this your format is not as you are saying
A(1,2) and B(3,4)then the cross joinwill perform it like this:
使用此格式，您的格式与您所说的不同，
A(1,2) and B(3,4)那么交叉连接将执行如下操作：
SELECT Table1.Col1, Table2.Col2
FROM Table1
CROSS JOIN Table2
(A*B)= (1,3),(1,4),(2,3),(2,4)
(A*B)= (1,3),(1,4),(2,3),(2,4)
回答by cxwangyi
mysql> select * from
-> (select 1 x union select 2 union select 3 union select 4) t
-> join
-> (select 1 y union select 2 union select 3) tt;
+---+---+
| x | y |
+---+---+
| 1 | 1 |
| 1 | 2 |
| 1 | 3 |
| 2 | 1 |
| 2 | 2 |
| 2 | 3 |
| 3 | 1 |
| 3 | 2 |
| 3 | 3 |
| 4 | 1 |
| 4 | 2 |
| 4 | 3 |
+---+---+
12 rows in set (0.00 sec)
Removing the word joingives exactly the same result.
删除这个词join会得到完全相同的结果。
select * from
(select 1 x union select 2 union select 3 union select 4) t,
(select 1 y union select 2 union select 3) tt;
