如何避免 SELECT 语句中用于排序的额外列到最终输出？答案

【问题标题】：How to avoid the extra column used for ordering in the SELECT statement to the final output?如何避免 SELECT 语句中用于排序的额外列到最终输出？
【发布时间】：2020-04-10 18:05:58
【问题描述】：

我有一个包含 ID, Workitem_Type, [STATUS], Workitem, CompletedDate, WORK, Log_createdDate 列的表 TestTable

数据如下：

+----+---------------+--------+-----------+-------------------------+-------+-------------------------+
| ID | Workitem_Type | STATUS | Workitem  |     CompletedDate       | WORK  |     Log_createdDate     |
+----+---------------+--------+-----------+-------------------------+-------+-------------------------+
|  1 | Remainder     | Pass   | Workitem1 | 2019-12-19 01:20:35.060 | Work1 | 2014-12-17 00:36:38.557 |
|  2 | Remainder     | Pass   | Workitem2 | 2019-12-19 01:20:35.060 | Work2 | 2015-12-17 00:36:38.557 |
|  3 | Remainder     | Pass   | Workitem3 | 2019-12-17 01:20:35.060 | Work3 | 2018-12-17 00:36:38.557 |
|  4 | Request       | Pass   | Workitem4 | 2019-12-18 01:20:35.060 | Work4 | 2017-12-17 00:36:38.557 |
|  5 | Remainder     | Pass   | Workitem5 | 2019-12-17 01:20:35.060 | Work5 | 2016-12-17 00:36:38.557 |
+----+---------------+--------+-----------+-------------------------+-------+-------------------------+

我必须根据Workitem_Type、CompletedDate 给予优先级，并且应该在单个查询中按相同的优先级和Log_createdDate 排序。所以输出应该如下所示：

+----+---------------+--------+-----------+-------------------------+-------+-------------------------+
| ID | Workitem_Type | STATUS | Workitem  |      CompletedDate      | WORK  |     Log_createdDate     |
+----+---------------+--------+-----------+-------------------------+-------+-------------------------+
|  1 | Remainder     | Pass   | Workitem1 | 2019-12-19 01:31:12.620 | Work1 | 2014-12-17 00:36:38.557 |
|  2 | Remainder     | Pass   | Workitem2 | 2019-12-19 01:31:12.637 | Work2 | 2015-12-17 00:36:38.557 |
|  5 | Remainder     | Pass   | Workitem5 | 2019-12-17 01:31:12.637 | Work5 | 2016-12-17 00:36:38.557 |
|  3 | Remainder     | Pass   | Workitem3 | 2019-12-17 01:31:12.637 | Work3 | 2018-12-17 00:36:38.557 |
|  4 | Request       | Pass   | Workitem4 | 2019-12-18 01:31:12.637 | Work4 | 2017-12-17 00:36:38.557 |
+----+---------------+--------+-----------+-------------------------+-------+-------------------------+

我尝试了以下查询：

SELECT  *, CASE WHEN Workitem_Type = 'Remainder' THEN 
               CASE WHEN CompletedDate > GETDATE() THEN 1 ELSE 2 END 
           ELSE 3 END AS [Priority] 
FROM TestTable
ORDER BY [Priority], Log_createdDate;

但我不希望Priority 列出现在我的输出中。那么在单个查询中是否可以在没有优先级列的情况下获得上述输出？

请找到db<>fiddle 。

【问题讨论】：

然后不要把它（Priority）放在你的SELECT中，把表达式放在你的ORDER BY中。
@Larnu 但我需要基于优先级列的排序
是的，所以只在ORDER BY 中表达。您订购的内容不必包含在 SELECT 中（对此有一些警告，但在此查询中没有）。
@Larnu 是的，根据sticky bit 的回答，使用ORDER BY 中的CASE WHEN 表达式解决了我的问题。也感谢您的评论。

标签： sql sql-server select sql-order-by sql-server-2017

【解决方案1】：

直接在ORDER BY子句中使用表达式即可。

SELECT * 
       FROM testtable
       ORDER BY CASE
                  WHEN workitem_type = 'Remainder' THEN 
                    CASE
                      WHEN completeddate > getdate() THEN
                        1
                      ELSE
                        2
                    END 
                  ELSE
                    3
                END,
                log_createddate;

编辑：（戈登）

您不需要嵌套CASE 表达式：

   ORDER BY (CASE WHEN workitem_type = 'Remainder' AND completeddate > getdate()
                  THEN 1
                  WHEN workitem_type = 'Remainder' 
                  THEN 2
                  ELSE 3
             END),
            log_createddate;

【讨论】：

谢谢！这是我使用单个查询（没有子查询）所期望的。我会在几分钟内接受。

【解决方案2】：

您可以将查询包含在子查询中，并明确列出您希望选择的字段，例如：

SELECT ID, Workitem_Type, STATUS, Workitem, CompletedDate, Work, Log_createdDate
FROM (
SELECT  *,CASE WHEN Workitem_Type = 'Remainder' THEN 
        CASE WHEN CompletedDate > GETDATE() THEN 1 ELSE 2 END 
    ELSE 3 END as [Priority] 
FROM TestTable
) as a
ORDER BY [Priority],
         Log_createdDate

【讨论】：

【解决方案3】：

您可以使用如下子查询：

select ID, Workitem_Type, STATUS
    , Workitem, CompletedDate
    , WORK, Log_createdDate 
 from (SELECT  *, CASE WHEN Workitem_Type = 'Remainder' THEN 
               CASE WHEN CompletedDate > GETDATE() THEN 1 ELSE 2 END 
           ELSE 3 END AS [Priority] 
       FROM TestTable
      ORDER BY [Priority], Log_createdDate)

【讨论】：