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#1
November 4th, 2004, 07:48 PM
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Comparison with NULL
The book Using Firebird by IBPhoenix is talking about comparison operators and it says ...
Quote:
What does this mean? I have a timestamp field which may be NULL or it may have a date in it. I want to do the comparison (NEW.FIELD <> OLD.FIELD) in a trigger. If one of these values is NULL what is the result of the comparison. I need the comparison above to return TRUE if OLD.FIELD = NULL and NEW.FIELD = a date. Please help me understand this.
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#2
November 5th, 2004, 02:55 AM
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Code:
NEW.FIELD <> OLD.FIELD will return UNKNOWN if either of the operands is null. Code:
NEW.FIELD <> OLD.FIELD or OLD.FIELD is null
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#3
November 6th, 2004, 12:40 AM
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In Firebird 1.5 (stable) you can compare it using construct like
COALESCE(new.field, 0) <> COALESCE(old.field, 0) In Firebird 2.0 (development) you can also use another standard SQL construct for the same purpose: new.field IS DISTINCT FROM old.field
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