NULLs and composite types

PostgreSQL 9.0.2 (CentOS 4.4):<br /><br /> I think the crux of my problem is:<br /><br /> SELECT ROW( NULL, NULL) IS
NULL; -- returns TRUE<br /><br /> SELECT COALESCE( ROW( NULL, NULL), ROW( 1,2 ));  -- returns "(,)"<br /><br />
Manifestation:<br/><br /> I have a composite type:<br /><br /> CREATE          TYPE    "BaseTypes"."GeoPosition" 
AS(<br/>         latitude        FLOAT,<br />         longitude       FLOAT<br /> );<br /><br /> For the problem at
hand,I have two tables (say named A and B) which each declare a field thusly:<br /><br />    ...<br />    location" 
"BaseTypes"."GeoPosition",<br/>    ...<br /><br /> I also have a PL/pqSQL TRIGGER (BEFORE INSERT) that intercepts
INSERTsto table A generated elsewhere, and depending on a bunch of stuff, may:<br /><br /><ol><li>Change values in NEW
fields.<li>Usinga CURSOR, go find a related record in table A and update that instead (and RETURN NULL from the TRIGGER
procedure),or just RETURN NEW.<li>Before RETURNing, the TRIGGER procedure may also INSERT or UPDATE a related record in
tableB.</ol><p>This has all worked beautifully for three years, until I added the above "location" variable to tables A
andB.  At the beginning of the TRIGGER procedure, I have:<br /><p>                IF  (NEW.location).latitude  IS NULL
OR (NEW.location).longitude IS NULL    THEN<br />                         NEW.location    := NULL;<br />
               END IF;<br /><p>My intent is to make sure that "location" never has the value "ROW( NULL, NULL)", mainly
forsubsequent rendering in a web page.<br /><p>This works in making sure that table A never has the above value. 
However,when I INSERT or UPDATE the related record in table B, somehow the fully "NULL" value for "location" gets
"corrupted"into "ROW( NULL, NULL)".  I've spent the better part of a day trying to figure this out, with statements
like("record_row" comes from a row captured in a CURSOR SELECT statement from table A):<br /><p>                       
IF (record_row.location).latitude  IS NULL OR  (record_row.location).longitude IS NULL  THEN<br />
                               record_row.location     := NULL;<br />                         END IF;<br />
                       IF  record_row.location = ROW( NULL, NULL )::"GeoPosition"      THEN<br />
                               RAISE   LOG     'Debug 1';<br />                         END IF;<br /><p>These are six
successivelines, and yet the RAISE statement is frequently executed.<br /><p>Right now I get rid of the problem by
manually(and frequently) executing the following statement:<br /><p>UPDATE "A" SET location = NULL WHERE location =
ROW(NULL, NULL )::"GeoPosition";<br /><p>The above changes the "corrupted" lines correctly, and DOESN'T change lines
where"location" is already fully NULL.<br /><p>What's going on?  I can provide more detail if requested.  Of course, an
obviousworkaround is to use in a VIEW:<br /><p>... NULLIF( location, ROW( NULL, NULL )::"GeoPosition" ) ...<br /><p>but
I'dlike to know the cause.<br /><p>ps: I know the word "location" is "non-reserved", and if that's the problem, I can
changeit;  it just means changing a bunch of other stuff, which I'd rather not do unless necessary.<p>-- Dean<br /><br
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