(mysql to postgresql) in php functions

Hi. I am migrating a site database from MySQL to PostgreSQL.

First I just changed the function calls and then I got the error
message that PHP was not compiled with PostgreSQL support.

Ok, so I recompiled the PHP as necessary and now the problem is that
there was a function being used, called mysql_select_db();, that there is
none to use with PostgreSQL instead of it.

I really dont know if it is necessary to use the select_db function
after the connection to the database. But I think so, because when I try to
execute a query (without running the select_db function) I get the error
message:

"Fatal error: Call to undefined function: pg_query() in
/path/file.php on line 123"

Anybody can help me? Although this is not a php mail list?! :-)

Tks,
Wagner