Question

Two quick (I hope!) questions:

Counting rows

Is it more efficient to use COUNT(id) in an SQL query, or to just select all the rows and use PHP’s mysql_num_rows() function on the returned resource? Would this depend on the size of the results query? Is there a fairly easy way of determining the answer to this question?

Results arrays

At the moment, I am using COUNT(id) in a query, and then obviously using mysql_query() and mysql_fetch_array(), as follows:

$sql = "SELECT COUNT(id) FROM TABLE1;";
$resource = mysql_query($sql) or die(mysql_error())
$result = mysql_fetch_array($resource);
$count = $result[0];

and this returns the number of rows fine. However, I’m surprised that

$count = mysql_fetch_array($resource)[0];

doesn’t work; I get the error:

Parse error: syntax error, unexpected '[' in C:\ServerDocs\file1.php on line 44 

is there an easy explanation as to what’s going on?

Thanks in advance,
Chris

Answer 1

1. It depends on the situation, but SELECT COUNT(*) is normally faster.
   The reason is simply that using mysql_num_rows(), the database
   server has to actually build the result set. With a COUNT(*), on the
   other hand, the DB may be able to determine the number of rows just
   from indexes, which is much faster. So if all you want is the count,
   then mysql_num_rows() ends up doing a lot more work for the same
   result.

   Another down side is that mysql_num_rows doesn’t work with
   unbuffered queries. So if you need to work with very large result
   sets, using mysql_num_rows might not be an option. However, COUNT(*)
   is always available.

2. $count = mysql_fetch_array($resource)[0];

   This type of statements are not possible in current version of php.
   So, better use

   $no_of_rows = mysql_fetch_array($count);
   echo $no_of_rows[0];