如何写这个选择陈述

Result for key2 = 2DataKey1Key2C12D2NUL 结果key2 = 3 Result for key2 =3DataKey1Key2B1NULLD2NULL 需要在用户定义的单一选择语句中使用将kye2作为参数的函数 我尝试过： 我已经尝试了几个语句，但是其中一个案例的每个人都失败了 非常感谢帮助这个It needs to be in single select statement to be used inside user defined function that taking kye2 as parameterWhat I have tried:I have tried several statements, but everyone fails for one of the casesWould appreciate help on this one推荐答案 我把它分解成了这两个部分 1 - 列 key2 的所有内容都与参数匹配 2 - 任何事情（请注意更改在措辞中）列 key2 为NULL且列 key1 未出现在上述1的结果中 然后我将其转换为两个公用表表达式并UNIONed结果：I broke this down into the two parts1 - Everything where column key2 matches the parameter2 - Anything (note the change in wording) where column key2 is NULL and column key1 does not appear in the results from 1 aboveI then converted that into two Common Table Expressions and UNIONed the results:;with CTE1 AS(SELECT 'CTE1' AS SOURCE, *FROM @tmp WHERE Key2 = @key), CTE2 AS(SELECT 'CTE2' AS SOURCE, *FROM @tmp WHERE Key2 IS NULLAND Key1 NOT IN (SELECT Key1 FROM CTE1))SELECT * FROM CTE1 UNION SELECT * FROM CTE2ORDER BY [Data]我收录了 SOURCE 专栏只是为了清楚数据实际来自哪里 - 你应该删除它。 在设置这个功能方面我的 @key 将是该函数的参数。如果你不熟悉这个函数，下面是一些关于如何设置函数的说明 - 实用示例的SQL Server表值函数 [ ^ ] 最后这里是我使用的测试数据，我需要回到这个问题:-) I included the SOURCE column just for clarity on where the data was actually coming from - you should remove it.In terms of setting this up as a function my @key would be the parameter to that function. Here are some instructions on how to set up a function if you are not familiar with that - SQL Server Table-Valued Function By Practical Examples[^] Finally here is the test data I used, in case I need to come back to this question :-)declare @tmp table ([Data] varchar(10),Key1 int, Key2 int)insert into @tmp ([Data], Key1, Key2) values('A',1,1), ('B',1,NULL), ('C',1,2), ('D',2,NULL), ('E',3,1)declare @key int set @key = 3 如果按键1进行分组，然后按key2 desc进行排序，然后选择顶部每组一个？What if you did group by key 1 and then order by key2 desc, and select the top one from each set? 这篇关于如何写这个选择陈述的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！