I am using:
PHP 5.2.10-dev (cli) (built: May 19 2009 15:40:36) 
and still get the same error result.

This error is also in the pg_update function, where NULl values are compared with "= NULL" rather than "IS NULL" in the WHERE part of the generated SQL.

For completeness, I get the error running on Fedora 10 with Postgres 8.3.5

Sorry, I think I posted my reply in the wrong place, so let me try again.

I have just downloaded and tested the latest PHP version:
PHP 5.2.10RC2-dev (cli) (built: May 31 2009 07:16:36)

With this version I still get the same error. The Postgresql version I am testing against is:
PostgreSQL 8.3.5 on i386-redhat-linux-gnu, compiled by GCC gcc (GCC) 4.3.2 20081007 (Red Hat 4.3.2-6)

The call to:
print(pg_delete($db,'demo',$row,PGSQL_DML_STRING)) 
still prints out:
DELETE FROM demo WHERE id=1 AND col1=NULL;

The final test should use the SQL language "IS NULL" test rather than "=NULL" which never evaluates to true.

The same problem exists if using pg_update, which produces:
UPDATE demo SET id=2,col1='Two' WHERE id=1 AND col1=NULL;

Again, "col1=NULL" will never evaluate to true using SQL, and the test col1 IS NULL should be used instead.

Patch for this bug:

http://news.php.net/php.internals/46974

This bug has been fixed in SVN.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
 
Thank you for the report, and for helping us make PHP better.

Thanks for the patch!

Hi,
I have just downloaded the latest 5.2 version from SVN, and tested this again. 
It is still 
not working. I have created a more complete test case that can be used.

===========Start===========
<?php

$linenum=0;
function _print($str) {
  global $linenum;
  print($linenum++."\t".$str."\n");
}

_print('PHP_VERSION : '.PHP_VERSION);
_print('PHP_OS : '.PHP_OS);

$db = pg_connect("dbname=test");
if (! $db) {
  die("Not connected");
}

//Create a test table
$create = 'create table testcase (id integer, col1 varchar(20))';
$result = pg_query($db,$create);

//Insert some test data
$row = array('id'=>1, 'col1'=>'I');
_print(pg_insert($db,'testcase',$row,PGSQL_DML_STRING));
pg_insert($db,'testcase',$row);
$row = array('id'=>2, 'col1'=>'');
_print(pg_insert($db,'testcase',$row,PGSQL_DML_STRING));
pg_insert($db,'testcase',$row);
$row = array('id'=>3, 'col1'=>null);
_print(pg_insert($db,'testcase',$row,PGSQL_DML_STRING));
pg_insert($db,'testcase',$row);

//Selects
$search = array('col1'=>'I');
_print(pg_select($db,'testcase',$search,PGSQL_DML_STRING));
$result = pg_select($db,'testcase',$search);
if ($result) {
  _print($result[0]['id']."\t".$result[0]['col1']);
} else {
  _print('Not found');
}
$search = array('col1'=>'');
_print(pg_select($db,'testcase',$search,PGSQL_DML_STRING));
$result = pg_select($db,'testcase',$search);
if ($result) {
  _print($result[0]['id']."\t".$result[0]['col1']);
} else {
  _print('Not found');
}
$search = array('col1'=>null);
_print(pg_select($db,'testcase',$search,PGSQL_DML_STRING));
$result = pg_select($db,'testcase',$search);
if ($result) {
  _print($result[0]['id']."\t".$result[0]['col1']);
} else {
  _print('Not found');
}

//Updates
$data = array('id'=>5);
$condition = array('col1'=>'I');
_print(pg_update($db,'testcase',$data,$condition,PGSQL_DML_STRING));
$condition = array('col1'=>'');
_print(pg_update($db,'testcase',$data,$condition,PGSQL_DML_STRING));
$condition = array('col1'=>null);
_print(pg_update($db,'testcase',$data,$condition,PGSQL_DML_STRING));

//Deletes
$condition = array('col1'=>'I');
_print(pg_delete($db,'testcase',$condition,PGSQL_DML_STRING));
$condition = array('col1'=>'');
_print(pg_delete($db,'testcase',$condition,PGSQL_DML_STRING));
$condition = array('col1'=>null);
_print(pg_delete($db,'testcase',$condition,PGSQL_DML_STRING));

//clean up
$drop = 'drop table testcase';
$result = pg_query($db,$drop);

=============End===============

The generated output from this script is:

0       PHP_VERSION : 5.2.16-dev
1       PHP_OS : Linux
2       INSERT INTO testcase (id,col1) VALUES (1,'I');
3       INSERT INTO testcase (id,col1) VALUES (2,'');
4       INSERT INTO testcase (id,col1) VALUES (3,NULL);
5       SELECT * FROM testcase WHERE col1='I';
6       1       I
7       SELECT * FROM testcase WHERE col1='';
8       2
9
10      Not found
11      UPDATE testcase SET id=5 WHERE col1='I';
12      UPDATE testcase SET id=5 WHERE col1='';
13      UPDATE testcase SET id=5 WHERE col1=NULL;
14      DELETE FROM testcase WHERE col1='I';
15      DELETE FROM testcase WHERE col1='';
16      DELETE FROM testcase WHERE col1=NULL;


Notes:
Line 0: php version 5.2.16-dev - latest version just downloaded.
Line 9: No SELECT string is generated if the parameter contains NULL
Line 10: No data is found when searching for NULL
Line 13: Still using col1=NULL instead of col1 IS NULL
Line 16: Still using col1=NULL instead of col1 IS NULL

Has the patch been merged with the version at snaps.php.net?

Hello, the fix was committed to 5.3.x branch and trunk, not to 5.2.x.

OK, Sorry. I have downloaded and tested 5.3.5 and this is working perfectly! 
Thanks for fixing this.