Question

我的查询出现以下错误：

here is an entry for table "table1", but it cannot be referenced from this part of the query.

这是我的疑问：

SELECT id 
FROM property_import_image_results table1
  LEFT JOIN (
    SELECT created_at 
    FROM property_import_image_results
    WHERE external_url = table1.external_url
    ORDER BY created_at DESC NULLS LAST 
    LIMIT 1
  ) as table2 ON (pimr.created_at = table2.created_at)
WHERE table2.created_at is NULL

Answer 1

您需要横向连接才能在连接的子选择中引用外部表。

您还在连接条件中引用别名pimr，这在查询中的任何位置都不可用。因此，您需要在连接条件中将其更改为table1。

您还应该在内部查询中为表格提供别名以避免混淆：

SELECT id 
FROM property_import_image_results table1
  LEFT JOIN LATERAL (
    SELECT p2.created_at 
    FROM property_import_image_results p2
    WHERE p2.external_url = table1.external_url
    ORDER BY p2.created_at DESC NULLS LAST 
    LIMIT 1
  ) as table2 ON (table1.created_at = table2.created_at)
WHERE table2.created_at is NULL

修改

这种查询也可以使用窗口函数来解决：

select id
from (
  select id,  
         max(created_at) over (partition by external_url) as max_created
  FROM property_import_image_results
) t
where created_at <> max_created;

此可能比聚合和加入更快。但这很难说。横向连接也非常有效。它的优点是您可以将任何列添加到结果中，因为不需要分组。

在查询的这一部分（子查询）错误中无法引用条目

1 个答案: