SQL拆分字符串并获取NULL值而不是空字符串 [英] SQL split string and get NULL values instead of empty string

问题描述

如何拆分字符串并获取NULL值而不是空字符串.

How to split string and get NULL values instead of empty string.

我对 STRING_SPLIT 和 XML 两种方法特别感兴趣.我希望这个查询:

I am particularly interested in two methods STRING_SPLIT and XML. I wish this query:

SELECT * FROM STRING_SPLIT('a,b,,d', ',');

将在第三行返回 NULL 而不是空字符串.有什么简单的方法可以实现它，即使用特殊字符?我的意思是:

would return in third row NULL instead of empty string. Is there any easy way to achieve it i.e. with special characters? I mean something like:

SELECT * FROM STRING_SPLIT('a,b,[null],d', ',') -- this, of course, wouldn't go

我希望我可以使用 XML 方法从字符串中提取 NULL:

I wish I could extract NULLs from string using XML method:

CREATE FUNCTION dbo.SplitStrings_XML
(
   @List       varchar(8000),
   @Delimiter  char(1)
)
RETURNS TABLE WITH SCHEMABINDING
AS
   RETURN (SELECT [value] = y.i.value('(./text())[1]', 'varchar(8000)')
      FROM (SELECT x = CONVERT(XML, '<i>' 
          + REPLACE(@List, @Delimiter, '</i><i>') 
          + '</i>').query('.')
      ) AS a CROSS APPLY x.nodes('i') AS y(i));

从这里抓取的代码:https://sqlperformance.com/2016/03/t-sql-queries/string-split

推荐答案

用NULLIF包裹返回值:

SELECT NULLIF([value],'') FROM STRING_SPLIT...

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