为什么我得到专栏＆＃34;结束＆＃34;不存在？

Question

我正在尝试在SQL中执行条件ORDER BY但是我收到错误：column "ended" does not exist指向＆＃34;结束＆＃34;＆＃39;＆＃39;查询的一部分。

这是我的问题：

SELECT (EXTRACT(EPOCH FROM SUBMISSION_DEADLINE)
       -EXTRACT(EPOCH FROM now())) AS "datediff"
    , (EXTRACT(EPOCH FROM SUBMISSION_DEADLINE)>EXTRACT(EPOCH FROM now())) AS "ended", *
FROM imdown_api_v1_contest
ORDER BY "ended" DESC, case when "ended" = true then "datediff" else "-datediff" END ASC;

我需要先抓住尚未结束的比赛，然后先按顺序结束。然后我需要所有已经结束的东西，并按最近结束的那些顺序排序。

Answer 1

执行order by时，未定义

列ended，sql按下一顺序执行查询：

从
2. ，其中
3. 顺序
4. 选择

因此，您需要将完整表达式复制到order by子句中或使用子查询，例如：

select * from (
    SELECT (EXTRACT(EPOCH FROM SUBMISSION_DEADLINE)-EXTRACT(EPOCH FROM now())) AS "datediff", (EXTRACT(EPOCH FROM SUBMISSION_DEADLINE)>EXTRACT(EPOCH FROM now())) AS "ended", *
    FROM imdown_api_v1_contest
) tmpq
ORDER BY "ended" DESC, case when "ended" = true then "datediff" else "-datediff" END ASC

Answer 2

您的查询在多个位置被破坏或效率低下，而不仅仅是对列别名的非法引用。这可能符合你的意图：

SELECT EXTRACT(EPOCH FROM now() - submission_deadline) AS datediff
     , now() > submission_deadline AS ended  -- I inverted your expression!
     , *
FROM   imdown_api_v1_contest
ORDER  BY 2  -- positional reference to output column
     , @(EXTRACT(EPOCH FROM now() - submission_deadline))

通常，竞赛结束＆＃34;在 过去 中有submission_deadline，所以now() > submission_deadline AS ended，而不是相反。

要修复主要语法错误，我使用位置引用而不是列别名。详细解释：

• PostgreSQL Where count condition

相关示例：

• PostgreSQL: running count of rows for a query 'by minute'

要获得所需的订单，请使用absolute value operator @。