check if SQL row exists with PHP

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.}

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;

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}