是否可以仅在 SQL 中测试空记录？

发布于 2024-10-11 19:10:54 字数 627 浏览 0 评论 0原文

我正在尝试帮助同事解决一个特殊问题，而她仅限于 MS SQL QUERY 代码。目的是如果查询没有返回记录，则插入虚拟记录（到周围的联合中）。

我在从 PL/SQL 到 MS SQL 之间来回切换时遇到了困难，我正在寻求帮助（我不是特别有吸引力，但我对 StackOverflow 观众很有吸引力）。

基本上，我们需要来自目标 Select ... 语句的单个可测试值。

理论上，它会这样做：

(other records from unions)
Union
   Select "These" as fld1, "are" as fld2, "Dummy" as fld3, "Fields" as fld4 
   where NOT (Matching Logic)
Union
   Select fld1, fld2, fld3, fld4  // Regular records exist
   From tested_table
   Where (Matching Logic)

无条件地强制单个虚拟记录是有效的。

有没有办法从 Select 中获得单一的、可测试的结果？

无法用代码实现（不允许），但可以提供 SQL

Anybody 吗？有人吗？贝勒？

原文

I am trying to help a co-worker with a peculiar problem, and she's limited to MS SQL QUERY code only. The object is to insert a dummy record (into a surrounding union) IF no records are returned from a query.

I am having a hard time going back and forth from PL/SQL to MS SQL, and I am appealing for help (I'm not particularly appealing, but I am appealing to the StackOverflow audiance).

Basically, we need a single, testable value from the target Select ... statement.

In theory, it would do this:

(other records from unions)
Union
   Select "These" as fld1, "are" as fld2, "Dummy" as fld3, "Fields" as fld4 
   where NOT (Matching Logic)
Union
   Select fld1, fld2, fld3, fld4  // Regular records exist
   From tested_table
   Where (Matching Logic)

Forcing an individual dummy record, with no conditions, works.

IS there a way to get a single, testable result from a Select?

Can't do it in code (not allowed), but can feed SQL

Anybody? Anybody? Bbeller?

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我三岁 2024-10-18 19:10:54

您可以将 unions 放入 with 中，然后包含另一个仅在大联合为空时返回 null 的联合：

; with BigUnion as
         (
         select  *
         from    table1
         union all
         select  *
         from    table2
         )
select   *
from     BigUnion
union all
select   null
where    not exists (select * from BigUnion)

You could put the unions in a with, then include another union that returns a null only when the big union is empty:

; with BigUnion as
         (
         select  *
         from    table1
         union all
         select  *
         from    table2
         )
select   *
from     BigUnion
union all
select   null
where    not exists (select * from BigUnion)

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