num_rows vs count()

[OwenTheSamoan]

using mysql with php. I have a very large table and I want to get the number of a specific amount from one of the fields. I can use two ways of getting this info, but would like to know which is the fastest and most efficient way. One way uses count() the other method uses num_rows. Thanks in advance.

$sql=mysql_query("select count(sentto) from mail where sentto ='$username' ");
$row = mysql_fetch_array($sql);
$username_check = $row['count(sentto)'];

echo "$username_check";

OR

$sql_sentto_check=mysql_query("select sentto from mail where sentto ='$username' ");
$username_check=mysql_num_rows($sql_sentto_check);

echo "$username_check";

[wilku]

imho it depends on if you need the data from the second query or not. If yes, then use the second method. If not, then use the first one. I suppose it would be quicker, because only one number has to be transfered from mysql to php, whereas in the second method the whole set of data is transfered (the query returns much more data).

[Weedpacket]

Also, using COUNT, the DBMS only needs to look at the index on mail.sentto (assuming that field has an index), not at the table data itself.

The general principle is to do database queries in the database. 🙂

[OwenTheSamoan]

Thank you very much guys!