In postgresql, you can do it like so:
$conn=pg_connect("host=server user=username dbname=mydb");
$res=pg_exec($conn,"select * from pg_tables where tablename not like 'pg_%'");
$rows = pg_numrows($res);
for ($i=0;$i<$rows;$i++){
$row = pg_fetch_array($res,$i,PGSQL_ASSOC);
print $row[tablename]."<BR>";