谁能解释一下如何从select中获取列的值，并将其赋值给postgres中的另一个select

Question

有人能解释一下如何将列的值从一个select传递到另一个select吗?在我的例子中，如何将值参数传递给名为“cad_products.id_product”的字段？

遵循代码。

SELECT
    json_agg ( T ) AS retorno 
FROM
    (
SELECT
    cad_products.*,
    json_agg ( b ) AS properties 
FROM
    cad_products,
    (
SELECT
    cad_properties.id_property,
    cad_properties.description 
FROM
    cad_products_properties
    LEFT JOIN cad_properties  ON cad_products_properties.id_property  = cad_properties.id_property  
WHERE
    cad_products_properties.id_product = **"parameter"**
    ) b 
WHERE
    cad_products.id_agr = 37
GROUP BY
    cad_products.id_product 
    ) T

Answer 1

很难说你的参数是什么，它来自哪里，但我建议在连接中处理它。此外，使用CTE可以在一定程度上提高可读性，如下所示：

WITH data AS
(
SELECT prod.*
     , json_object_agg(prop.id_property, prop.description) AS properties
  FROM cad_products prod
  JOIN cad_products_properties cpp ON (cpp.id_product = prod.id_product) -- Not sure what your parameter is
  LEFT JOIN cad_properties prop ON (cpp.id_property = prop.id_property)
) SELECT JSON_AGG(data) AS retorno;