check if SQL row exists with PHP

问题:

I'm using MySQL with PHP and I need to do something like this (pseudocode):

if (sql row exists where username='bob') {     // do this stuff } 

回答1:

If you are using mysql database, then use the following -

$query = "SELECT username from my_table where username='bob'"; $result = mysql_query($query);  if(mysql_num_rows($result) > 0) {     // row exists. do whatever you would like to do. } 

If you would like to use PDO (PHP Data Object), as alex suggested, then use the following code -

$dbh = new PDO("mysql:host=your_host_name;dbname=your_db_name", $user, $pass); $stmt = $dbh->prepare("SELECT username from my_table where username = ':name'"); $stmt->bindParam(":name", "bob"); $stmt->execute();  if($stmt->rowCount() > 0) {     // row exists. do whatever you want to do. } 

回答2:

Sayem's answer has the most upvotes, but I believe it is incorrect regarding PDO.

From the PHP docs:

For most databases, PDOStatement::rowCount() does not return the number of rows affected by a SELECT statement. Instead, use PDO::query() to issue a SELECT COUNT(*) statement with the same predicates as your intended SELECT statement, then use PDOStatement::fetchColumn() to retrieve the number of rows that will be returned.

$sql = "SELECT COUNT(*) FROM fruit WHERE calories > 100"; if ($res = $conn->query($sql)) {    /* Check the number of rows that match the SELECT statement */   if ($res->fetchColumn() > 0) {         /* Issue the real SELECT statement and work with the results */        $sql = "SELECT name FROM fruit WHERE calories > 100";        foreach ($conn->query($sql) as $row) {            print "Name: " .  $row['NAME'] . "\n";        }   }   /* No rows matched -- do something else */   else {       print "No rows matched the query.";   } }  $res = null; $conn = null; 

回答3:

another approach

$user = "bob"; $user = mysql_real_escape_string($user); $result = mysql_query("SELECT COUNT(*) AS num_rows FROM my_table WHERE username='{$user}' LIMIT 1;"); $row = mysql_fetch_array($result); if($row["num_rows"] > 0){    //user exists } 

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