Question

我下面有两个表：

表A

+--------+--------+--------+
| color  | shape  |  size  |
+--------+--------+--------+
| Red    | Square | Small  |
| Blue   | Square | Small  |
| Yellow | Square | Small  |
| Red    | Circle | Small  |
| Blue   | Circle | Small  |
| Yellow | Circle | Small  |
| Yellow | Square | Medium |
| Red    | Circle | Medium |
| Blue   | Circle | Medium |
| Yellow | Circle | Medium |
| Red    | Square | Large  |
| Red    | Circle | Large  |
| Blue   | Circle | Large  |
| Yellow | Circle | Large  |
+--------+--------+--------+

表B

+---------------+
|     edge      |
+---------------+
| Straight Line |
| Dotted Line   |
| Squiggly Line |
+---------------+

我正在运行以下查询：

WITH TableA (color, shape, size)
AS (SELECT DISTINCT color, shape, size
     FROM   TableA),

TableB (edge)
AS (SELECT DISTINCT edge
    FROM   TableB)

SELECT COUNT(*) FROM 
(SELECT  a.*,
         b.*
FROM     TableA AS a
         CROSS JOIN TableB AS b) as x;

我希望发生的事情：它将从表A的每一列中选择所有不同的值（颜色，形状，大小），然后从表B的每一列中选择每个唯一值（边），然后进行交叉联接产生颜色，形状，大小和边缘的每种组合。

我检查了查询选择唯一值的部分是否可以独立工作，但是一起运行将产生比我预期更少的行。

使用3种颜色，2种形状，3种尺寸和3条边缘，我应该得到54种可能的组合/行，但只有42种。

Answer 1

您需要独立选择列：

select c.olor, s.shape, sz.size, e.edge
from (select distinct color from a) c cross join
     (select distinct shape from a) s cross join
     (select distinct size from a) sz cross join
     (select distinct edge from b) e

交叉连接返回的行太少

1 个答案: