2個數組中相同索引的元素的產品

Question

我需要乘以2個數組中的每個元素並投影一個數組，其中每個元素是產品結果。

例子：

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} | 

和查詢：

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} | 

我需要結合兩個查詢（交叉連接），並生成內部產品的每個doc和query_id的結果數組。

我第一次嘗試這樣一條：

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

然而，它產生這樣的錯誤：

Functions and operators can take at most one set argument

Answer 1

可以使用unnest()功能的方便的功能並行UNNEST多個陣列。

做，在一個LATERAL加入，每乘結果行和飼料，爲數組構造：

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; 

這是假設所有的數組的長度相同，否則多餘的元素都充滿了NULL。

相關：

• Unnest multiple arrays in parallel

所得數組中的順序對應於元素的原始順序。但考慮：

• PostgreSQL unnest() with element number