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[web] PHP/MySQL - Help with SELECT query

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Given the following PHP code:
$result = mysql_query("SELECT * FROM messages WHERE topic=" .$topic . " AND post=" . $post . " LIMIT 0,1"); if(!$result)
{
die();
}

Will die() be executed if zero rows are returned by the query? I'm writing a function where I want to check if a record does not exist within my database given the two parts of the primary key and I need to be able to differentiate between three cases: internal error (i.e. from mysql_query); 0 rows found; and 1 row found.

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I believe that a valid resource will be returned even if there are 0 rows. That is, mysql_query should only return false when an error (e.g. syntax, permission) occurs.

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You could try something like this -
$query = 'blah';$result = mysql_query( $query ) or die( 'internal error in the query' );if ( mysql_num_rows($result ) == 0 ) {    // 0 rows returned}else if ( mysql_num_rows( $result ) == 1 ) { // 1 row returned}mysql_free_result($result );

Alternatively, you could change your SQL around a little to make it a little cleaner -
$query = 'SELECT COUNT(*) as count FROM messages WHERE blah blah blah';$result = mysql_query( $querey ) or die( 'internal error in the query' );// COUNT(*) is guarenteed to return a single row, so you shouldn't// need to check if the row is valid. I think.$row = mysql_fetch_array( $result, MYSQL_ASSOC );if ($row['count'] == 0 ) {    // 0 rows will be returned}else if ( $row['count'] == 1 ) { // 1 row returned}mysql_free_result($result );

The second one is really only useful if you're not interested in the contents of the rows, since it just fetches the count. On the other hand, if all you want is the count, doing a SELECT * is kind of wasteful.