[QGIS-trac] Re: [Quantum GIS] #2974: Search for NULL value seemignly not possible from simple search and not obvious from advanced search

[Quantum GIS]

#2974: Search for NULL value seemignly not possible from simple search and not
obvious from advanced search
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   Reporter:  Elgon                             |              Owner:  nobody       
       Type:  bug                               |             Status:  new          
   Priority:  major: does not work as expected  |          Milestone:  Version 1.6.0
  Component:  Build/Install                     |            Version:               
   Keywords:  NULL search                       |   Platform_version:  Windows 7    
   Platform:  Debian                            |           Must_fix:  Yes          
Status_info:  0                                 |  
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Comment(by wonder):

 I disagree with the second suggestion: allowing the syntax "Field = NULL"
 would not be correct. We are trying to keep the functionality as close to
 SQL standard as possible. SQL uses three-valued logic (true, false,
 unknown) and all predicates like "x = NULL" return unknown. Select command
 returns only rows where predicate evaluates to true. Therefore "select *
 from Table WHERE x = NULL" will always return zero rows. Test for NULL can
 be done only by using "x IS NULL".

 If the user wants to search for NULL rows, we could allow him to enter
 "NULL" as a search text and generate the query as "x IS NULL".

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Ticket URL: <https://trac.osgeo.org/qgis/ticket/2974#comment:1>
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