Question

I’m using PostgreSQL 8.1, and I have two databases with one table names clients that are identical and contain +-50k rows each.

I need to obtain all ids in one table that aren’t in the other, I have the following solution

$sql = "SELECT id FROM clients WHERE id NOT IN(".pg_query($conn1,'SELECT id FROM clients').")";
$result = pg_query($conn2,$sql);

Before I run this, is this a good way to do it via PHP or are the other better faster ways?

Unfortunately I cant use dblink since I do not have privileges to install it.

Answer 1

If you can’t use a database link I think you will have to do it in the middleware – and this middleware should have a lot of RAM.

I would also recommend not to use PHP for this purpose, but if you have no other possibility, I would do it like this:

$ids = array();
$idsNotExist = array();
$resultDb1 = pg_query('SELECT id FROM db1');
while ( $row = pg_fetch_dontknowtheexactfunction_row($resultDb1) ) {
  array_push($ids, $row['id']);
}

$resultDb2 = pg_query('SELECT id FROM db2');
while ( $row = pg_fetch($resultDb2) ) {
  if ( !in_array($ids, $row['id']) ) {
    array_push($idsNotExist, $row['id']);
  }
}

Best way would of course be, because ID is primary key, to write an own in_array-function which removes the ID from haystack when it’s found because it will not be searched for again and the next search loop will be a bit faster.