正确的方式来询问是否mysql_num_rows在PHP

Question

因为mysql_num_rows如果没有返回任何行返回false，那么最好这样做:

$query = mysql_query("SELECT id FROM table WHERE something = 'this'"); 
$result = mysql_num_rows($query);
if ($result) { }

或者我应该这样做:

if ($result >= 1) { }

Answer 1

正确的方法是使用PDO而不是古老的mysql_*函数:

$stmt = $dbh->prepare('SELECT item_id FROM Items WHERE name = :param');
$stmt->bindParam( ':param', $some_name, PDO::PARAM_STR, 127 );
if ( $stmt->execute() )
{
   echo $stmt->rowCount();
   var_dump( $stmt->fetchAll( PDO::FETCH_ASSOC ));
}

Answer 2

正确的

$result = mysql_query("SELECT id FROM table WHERE something = 'this'"); 
if (mysql_num_rows($result)){
    //there are results
}

但是，您可以更轻松地完成此操作，而无需检查

。

$result = mysql_query("SELECT id FROM table WHERE something = 'this'"); 
while($row = mysql_fetch_assoc($result))
    //there are results
}

请

。给变量起一个合适的名字

Answer 3

如果没有返回行，则不返回false，在错误的情况下返回false。你可以这样处理:

 if ($result === false) {
    /* An error occurred - do something */
 } else {
    /* $result is set to some number >= 0 */
 }

Answer 4

说实话

$query = mysql_query("SELECT id FROM table WHERE something = 'this'"); 
if (mysql_num_rows($query)!==FALSE){
    //there are results
}

Answer 5

Count将返回一个值，并且您不能计数然后调用mysql_num_rows。

你可以做

$isExist = mysql_query("Select count(id) from ..."); 
$r = mysql_fetch_array($isExist);
if($r['COUNT(id)'] > 0){
//item exists
}else{
//item doesnt exist
}

或者你可以这样做:

$isexist = mysql_query("select * from wcddl_filehosts where downloadid = '".$download[id]."'");
if(mysql_num_rows($isExists)>0){
//we have items
}else{
//we dont have items
}