Description:
------------
According to the manual, pg_affected_rows should returns "the number of tuples 
(instances/records/rows) affected by INSERT, UPDATE, and DELETE queries.". The 
manual details : "The number of rows affected by the query. If no tuple is 
affected, it will return 0.".

PHP pg_affected_rows uses libpq's PQcmdTuples() to implement this:

  PHP_FUNCTION(pg_affected_rows)
  {
     
php_pgsql_get_result_info(INTERNAL_FUNCTION_PARAM_PASSTHRU,PHP_PG_CMD_TUPLES);
  }

  static void php_pgsql_get_result_info(INTERNAL_FUNCTION_PARAMETERS, int 
entry_type)
  {
  [...]
        case PHP_PG_CMD_TUPLES:
            Z_LVAL_P(return_value) = atoi(PQcmdTuples(pgsql_result));

But server's answers to PQcmdTuples() commands changed since PostgreSQL 9.0. 
When executed after a SELECT, PostgreSQL < 9.0 returned 0 (as in "0 rows were 
affected"); starting with PostgreSQL 9.0, the server returns the number of 
SELECTed rows.

See how the PQcmdTuples documentation was updated after pg 9:
http://www.postgresql.org/docs/8.4/interactive/libpq-exec.html#LIBPQ-EXEC-
SELECT-INFO
http://www.postgresql.org/docs/9.1/interactive/libpq-exec.html#LIBPQ-EXEC-
SELECT-INFO

PostgreSQL C API doesn't actually offers a "tell me how many rows were 
written/modified" function.  But we can restore the previous pg_affected_rows 
behavior, and enjoy consistent results no matter which server version we run 
against, by unconditionally returning 0 after a SELECT.

This is what the attached patch does, identifying the SELECT with 
PQresultStatus() value (which returns PGRES_COMMAND_OK after a successful DML, 
as opposed to PGRES_TUPLES_OK after a SELECT, etc).

If you ask so, I can also provide an alternative patch (which tests the string 
returned by PQcmdStatus(), a bit ugly imo) and/or an unit test script for PHP's 
test framework.


Test script:
---------------
// Bug on a PostgreSQL >= 9.0 server, ok on older versions.
$dbh = pg_pconnect("dbname=postgres host=localhost user=postgres port=5432");
$q = pg_query($dbh, "SELECT * from generate_series(1, 42);");
var_dump(pg_affected_rows($q));

Expected result:
----------------
int(0)

Actual result:
--------------
int(42)