Question

我需要将2个数组的每个元素相乘并投影一个数组，每个元素都是产品结果。

示例：

select * from vetor_query;

返回：

query_id |pesos                                                                                               |
---------|----------------------------------------------------------------------------------------------------|
1        |{2.0000,0.4150,2.0000,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000} |

查询：

select * from vetor_documento;

返回：

doc    |pesos                                                                                               |
-------|----------------------------------------------------------------------------------------------------|
d1.txt |{3.0000,0.8301,4.0000,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000} |
d2.txt |{2.0000,0.0000,0.0000,0.0000,2.0000,2.0000,2.0000,2.0000,2.0000,0.0000,0.0000,0.0000,0.0000,0.0000} |
d3.txt |{0.0000,1.0729,0.0000,0.0000,0.0000,0.0000,2.0000,1.0000,0.0000,2.0000,2.0000,0.0000,0.0000,0.0000} |
d4.txt |{0.0000,1.0729,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000,0.0000,5.1699,4.0000,4.0000} |

我需要结合两个查询（交叉连接）并为每个doc和query_id生成内部产品的结果数组。

我的第一次尝试就是这个：

select vq.query_id, vd.doc, unnest(vq.pesos) * unnest(vd.pesos)
from vetor_query vq
cross join vetor_documento vd;

然而，它会产生此错误：

函数和运算符最多可以使用一个集合参数

Answer 1

您可以使用unnest()函数的便捷功能来并行删除多个数组。

在LATERAL联接中执行此操作，将每个结果行相乘并将其提供给ARRAY构造函数：

SELECT q.query_id, d.doc, qd.prod
FROM   vetor_query          q
CROSS  JOIN vetor_documento d
CROSS  JOIN LATERAL (
   SELECT ARRAY(SELECT x*y FROM unnest(q.pesos, d.pesos) t(x, y)) AS prod
   ) qd;

这假设所有数组都具有相同的长度，否则剩余元素用NULL填充。

2个数组中具有相同索引的元素的乘积

1 个答案: