PostgreSQL - 列不存在错误：列“ins_file_url”不存在[重复]答案

【问题标题】：PostgreSQL - column does not existERROR: column "ins_file_url" does not exist [duplicate]PostgreSQL - 列不存在错误：列“ins_file_url”不存在[重复]
【发布时间】：2021-01-21 09:03:48
【问题描述】：

我在 PostgreSQL 中有这个查询：

SELECT cars.*,
       manufacturers.company_name AS manufacturer_company_name,
       companies.mailing_name AS company_mailing_name,
       (SELECT car_documents.file_url FROM car_documents
         WHERE car_documents.car_id = cars.id AND car_documents.document_type = 1 LIMIT 1) AS ins_file_url,
       (SELECT car_documents.file_url FROM car_documents
         WHERE car_documents.car_id = cars.id AND car_documents.document_type = 3 LIMIT 1) AS guar_file_url,
       FROM "cars" 
       INNER JOIN "companies" ON "companies"."id" = "cars"."company_id" 
       LEFT JOIN shippers ON shippers.id = cars.shipper_id 
       WHERE (cars.status IS NULL
                AND cars.delivered < '2021-01-14'
                AND ins_file_url IS NOT NULL)

为什么我不能在WHERE 子句中使用别名列ins_file_url？这种行为有什么解决方法吗？

提前谢谢你

【问题讨论】：

想象一下，您在某个表中有相同的列，并有一个具有该名称的别名。 DBMS 应该如何知道，列是什么？好的，通过子查询你可以使用像tableAlias.columnName 这样的表别名，但是对于本地计算的列（即在select 列表中）你应该怎么做呢？

标签： sql postgresql column-alias

【解决方案1】：

只需在子查询中使用您的整个查询并在子查询上应用where 条件，如下所示：

Select * from
(SELECT cars.*,
       manufacturers.company_name AS manufacturer_company_name,
       companies.mailing_name AS company_mailing_name,
       (SELECT car_documents.file_url FROM car_documents
         WHERE car_documents.car_id = cars.id AND car_documents.document_type = 1 LIMIT 1) AS ins_file_url,
       (SELECT car_documents.file_url FROM car_documents
         WHERE car_documents.car_id = cars.id AND car_documents.document_type = 3 LIMIT 1) AS guar_file_url,
       FROM "cars" 
       INNER JOIN "companies" ON "companies"."id" = "cars"."company_id" 
       LEFT JOIN shippers ON shippers.id = cars.shipper_id
       WHERE cars.status IS NULL
         AND cars.delivered < '2021-01-14' ) t
   Where ins_file_url IS NOT NULL

【讨论】：

【解决方案2】：

尝试在别名周围使用双引号：

SELECT cars.*,
       manufacturers.company_name AS manufacturer_company_name,
       companies.mailing_name AS company_mailing_name,
       (SELECT car_documents.file_url FROM car_documents
         WHERE car_documents.car_id = cars.id AND car_documents.document_type = 1 LIMIT 1) AS ins_file_url,
       (SELECT car_documents.file_url FROM car_documents
         WHERE car_documents.car_id = cars.id AND car_documents.document_type = 3 LIMIT 1) AS guar_file_url,
       FROM "cars" 
       INNER JOIN "companies" ON "companies"."id" = "cars"."company_id" 
       LEFT JOIN shippers ON shippers.id = cars.shipper_id 
       WHERE (cars.status IS NULL
                AND cars.delivered < '2021-01-14'
                AND "ins_file_url" IS NOT NULL)

【讨论】：

它和未引用的一样