How to test for existence of nothing

Richard Durbin rd at sanger.ac.uk
Mon Jul 23 03:17:15 EST 2001

You can do this with the query "FIND Sequence Homol AND NOT NEXT".


Keith Bradnam wrote:
> Any acedb query gurus out there who can help me with a problem?
> It might be that it's beyond the capabilities of the acedb query language
> in which case Ed will set me straight.
> How do you test for the absence of a value in a tag-value pair where you
> would normally expect a value?
> E.g. we have sequence objects with Homol tags.  Associated with the Homol
> tag should be the name of a Sequence object.  Occasionally though, errors
> creep in where we lose the object and are left with just a tag.
> I would ideally like to be able to query the database to find errant
> entries like this.  I thought I might be able to get away with things like
> Find Sequence Homol AND NEXT = ""
> But (perhaps obviously) the 'AND NEXT' can't actually step any further to
> the right as there is nowhere to go.
> Maybe I should be looking into the dark murky world of AQL queries?
> I guess I want a perl style 'if (defined($tag))' to test for the presence
> (or absence) of a value for any specified tag.
> Any ideas anyone?  This would be really useful to me if it is possible.
> Keith
> ~  Keith Bradnam - WormBase group: http://wormbase.sanger.ac.uk/
> ~
> ~  The Sanger Centre, Wellcome Trust Genome Campus
> ~  Hinxton, Cambridge, CB10 1SA, UK.  Tel (01223) 497516

Richard Durbin                                      The Sanger Centre
email: rd at sanger.ac.uk                   Wellcome Trust Genome Campus
http://www.sanger.ac.uk/Users/rd/                             Hinxton
phone: 01223 494978                                Cambridge CB10 1SA
fax: 01223 494919                                                  UK

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