sql - NOT IN clause and NULL values -


This issue came when I got separate records, which I thought was a not where constraint and another one runs away . There was a zero value (poor data) in the table in the no constraint, due to which the query was returned to the count of 0 records. I understand why I can help fully understand some concept.

It just tells, why the results of Curie A result a result but B does not?

  A: Select 'right' where in 3 (1, 2, 3, zero) B: Select 'right' where not in 3 (1, 2, blank) < / Code> 

It was turned on SQL Server 2005. I also came to know that it happens to return the result code to set ansi_nulls off .

query A is the same:

  select 'true' where 3 = 1 or 3 = 2 or 3 = 3 or 3 = zero  

Since 3 = 3 is true, you get results.

The query B is the same:

  'true' where 3 & lt; & Gt; 1 & 3 & lt; & Gt; 2 and 3 & lt; & Gt; Blank  

when ansi_nulls is turned on, 3 ; Gt; Zero is unknown, therefore evaluates to invalidate the predicate, and you do not get any rows.

When ansi_nulls is closed, 3 & lt; & Gt; ; Blank is true, so the evaluation of reality is real, and you get a line.


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