交叉联接返回的行太少

Question

下面有两个表格：

Table一个

+--------+--------+--------+
| 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  |
+--------+--------+--------+

Table B

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

我是运行以下查询：

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;

我期望发生的事情：它将 select 来自 Table A（颜色、形状、大小）中每一列的所有不同值，然后 select 每个唯一值来自Table B（边）中的每一列，然后进行交叉连接，生成颜色、形状、大小和边的每种组合。

我已经检查了查询 select 的唯一值所在的部分是独立工作的，但是运行它一起产生的行数比我预期的要少。

有 3 种颜色、2 种形状、3 种尺寸和 3 条边，我应该得到 54 种可能 combinations/rows，但我只得到 42 种。

Answer 1

您需要独立 select 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

交叉联接返回的行太少

Cross join returning too few rows

sql

postgresql-9.6

cross-join