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(at)wareonearth(dot)com]
<mailto:[SMTP:gwaldron(at)wareonearth(dot)com]>
Sent: Tuesday, April 13, 1999 9:26 AM
To: pgsql-sql(at)postgreSQL(dot)org <mailto:pgsql-sql(at)postgreSQL(dot)org>
Subject: [SQL] Trouble with null text fields

Using Postgres 6.5 beta (snap 12 apr), on Linux i386. I moved up
from
6.4.2 when I couldn't get things working.
I'm having difficulty dealing with null text/varchar fields. I need to be
able to interpret null values as the null string " for the purposes 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
fields
is null, it is interpreted as the empty string " and the correct
answer
is 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
result
with 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 the
string
is null. Never could successfully do a null test on a function
parameter.

4) ----
I also tried writing my own concat function, and found that passing
null fields into a user function doesn't seem to work either. So I
tried
passing the whole thing in as a TUPLE, since you can determine
whether a
field 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