pg_fetch_assoc() returns an associative array that corresponds to the fetched row (tuples/records). It returns FALSE, if there are no more rows.
pg_fetch_assoc() is equivalent to calling pg_fetch_array() with PGSQL_ASSOC for the optional third parameter. It only returns an associative array. If you need the numeric indices, use pg_fetch_row().
row is row (record) number to be retrieved. First row is 0.
pg_fetch_assoc() is NOT significantly slower than using pg_fetch_row(), while it provides a significant ease of use.
See also pg_fetch_row(), pg_fetch_array(), pg_fetch_object() and pg_fetch_result().