How to get the total number of rows of a GROUP BY query?

Question

From the PDO manual:

PDOStatement::rowCount() returns the number of rows affected by the last DELETE, INSERT, or UPDATE statement executed by the corresponding PDOStatement object.

If the last SQL statement executed by the associated PDOStatement was a SELECT statement, some databases may return the number of rows returned by that statement. However, this behaviour is not guaranteed for all databases and should not be relied on for portable applications.

I found that out only very recently. I had just changed my db abstraction layer to not use SELECT COUNT(1) ... anymore, because just quering the actual rows and then counting the result would be much more efficient. And now PDO doesn't support that!?

I don't use PDO for MySQL and PgSQL, but I do for SQLite. Is there a way (without completely changing the dbal back) to count rows like this in PDO? In MySQL, this would be something like this:

$q = $db->query('SELECT a, b, c FROM tbl WHERE oele = 2 GROUP BY boele');
$rows = $q->num_rows;
// and now use $q to get actual data

With the MySQLi and PgSQL drivers, this is possible. With all PDO it isn't!?

PS. My initial solution was to extend the SQLResult->count method (my own) to replace SELECT ... FROM by SELECT COUNT(1) FROM and just return that number (very inefficient, but only for SQLite PDO). That's not good enough though, because in the example query above is a GROUP BY, which would change the meaning/function of the COUNT(1).

Answer 1

Here is the solution for you

$sql="SELECT count(*) FROM [tablename] WHERE key == ? "; $sth = $this->db->prepare($sql); $sth->execute(array($key)); $rows = $sth->fetch(PDO::FETCH_NUM); echo $rows[0]; 

Answer 2

It's a little memory-inefficient but if you're using the data anyway, I use this frequently:

$rows = $q->fetchAll();
$num_rows = count($rows);

Answer 3

The method I ended up using is very simple:

$query = 'SELECT a, b, c FROM tbl WHERE oele = 2 GROUP BY boele';
$nrows = $db->query("SELECT COUNT(1) FROM ($query) x")->fetchColumn();

Might not be the most efficient, but it seems to be foolproof, because it actually counts the original query's results.