RE: [SQL] Trouble with null text fields

Try this:

DROP FUNCTION nz(text);
CREATE FUNCTION nz (text) RETURNS text AS '  BEGIN     if ($1 is NULL) then        return '''';     else         return
$1;    end if;  END; ' LANGUAGE 'plpgsql';
 

SELECT (nz(field_one) || nz(field_two)) from t1;

This has worked for me.  It is a little slow. 
-----Original Message-----From:    Glenn Waldron [SMTP:gwaldron@wareonearth.com]Sent:    Tuesday, April 13, 1999 9:26
AMTo:   pgsql-sql@postgreSQL.orgSubject:    [SQL] Trouble with null text fields
 
Using Postgres 6.5 beta (snap 12 apr), on Linux i386.  I moved up
from6.4.2 when I couldn't get things working.
I'm having difficulty dealing with null text/varchar fields.  I needto be able to interpret null values as the null
string'' for thepurposes on concatenation.
 

1) ----For example, the query:
    SELECT (field_one || field_two) from t1;
Will return the concatenation of the two fields.  If either of the
fieldsis null, it is interpreted as the empty string '' and the correct
answeris printed.  But:
    SELECT * from t1 where ( field_one || field_two = 'something' )
This does NOT work is either field_one or field_two is null.  Same
resultwith the textcat() function.

2) ----Next I tried using "case", getting a parse error at or near "then":
    SELECT ( case field_one when null then '' else field_one end )
from t1;
This one gave me "ERROR: copyObject: don't know how to copy 704":
    SELECT ( case field_one when 'string' then 'other' else 'third'
end)from t1;


3) ---I tried writing a function that takes a "text" type and returns ''
is thestringis null.  Never could successfully do a null test on a function
parameter.

4) ----I also tried writing my own concat function, and found that passingnull fields into a user function doesn't seem
towork either.  So I
 
triedpassing the whole thing in as a TUPLE, since you can determine
whether afield is null with the GetAttributeByName() call.
The creation:
    CREATE FUNCTION mycat(text,text) returns text as
'/usr/.../file.so'langauge 'sql';
This worked great, even with null values:
    SELECT mycat(field_one, field_two) from t1;
This crashed the backend, with a "Memory exhauted in
AllocSetAlloc()" error:
    SELECT * from t1 where mycat(field_one, field_two) =
'something';
So I tried making an index, and got:  "DefineIndex(): Attibute t1
not found"
    CREATE INDEX t1_ix on t1 ( mycat(t1) text_ops );

Any help is appreciated!! Sorry for the novel!!  -glenn