Pulling data from Input Field From Mysql [duplicate] - php

Question

I need help checking if a row exists in the database. In my case, that row contains an email address. I am getting the result:
email no longer exists publisher#example.com
This is the code I'm currently using:
if (count($_POST)) {
$email = $dbl->real_escape_string(trim(strip_tags($_POST['email'])));
$query = "SELECT `email` FROM `tblUser` WHERE `email` = '$email'";
$result = mysqli_query($dbl, $query);
if (is_resource($result) && mysqli_num_rows($result) == 1) {
$row = mysqli_fetch_assoc($result);
echo $email . " email exists " . $row["email"] . "\n";
} else {
echo "email no longer exists" . $email . "\n";
}
}
Is there a better way to check if a row exists in MySQL database (in my case, check if an email exists in MySQL)?

Answer 1

The following are tried, tested and proven methods to check if a row exists.
(Some of which I use myself, or have used in the past).
Edit: I made an previous error in my syntax where I used mysqli_query() twice. Please consult the revision(s).
I.e.:
if (!mysqli_query($con,$query)) which should have simply read as if (!$query).
I apologize for overlooking that mistake.
Side note: Both '".$var."' and '$var' do the same thing. You can use either one, both are valid syntax.
Here are the two edited queries:
$query = mysqli_query($con, "SELECT * FROM emails WHERE email='".$email."'");
if (!$query)
{
die('Error: ' . mysqli_error($con));
}
if(mysqli_num_rows($query) > 0){
echo "email already exists";
}else{
// do something
}
and in your case:
$query = mysqli_query($dbl, "SELECT * FROM `tblUser` WHERE email='".$email."'");
if (!$query)
{
die('Error: ' . mysqli_error($dbl));
}
if(mysqli_num_rows($query) > 0){
echo "email already exists";
}else{
// do something
}
You can also use mysqli_ with a prepared statement method:
$query = "SELECT `email` FROM `tblUser` WHERE email=?";
if ($stmt = $dbl->prepare($query)){
$stmt->bind_param("s", $email);
if($stmt->execute()){
$stmt->store_result();
$email_check= "";
$stmt->bind_result($email_check);
$stmt->fetch();
if ($stmt->num_rows == 1){
echo "That Email already exists.";
exit;
}
}
}
Or a PDO method with a prepared statement:
<?php
$email = $_POST['email'];
$mysql_hostname = 'xxx';
$mysql_username = 'xxx';
$mysql_password = 'xxx';
$mysql_dbname = 'xxx';
try {
$conn= new PDO("mysql:host=$mysql_hostname;dbname=$mysql_dbname", $mysql_username, $mysql_password);
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $e) {
exit( $e->getMessage() );
}
// assuming a named submit button
if(isset($_POST['submit']))
{
try {
$stmt = $conn->prepare('SELECT `email` FROM `tblUser` WHERE email = ?');
$stmt->bindParam(1, $_POST['email']);
$stmt->execute();
while($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
}
}
catch(PDOException $e) {
echo 'ERROR: ' . $e->getMessage();
}
if($stmt->rowCount() > 0){
echo "The record exists!";
} else {
echo "The record is non-existant.";
}
}
?>
Prepared statements are best to be used to help protect against an SQL injection.
N.B.:
When dealing with forms and POST arrays as used/outlined above, make sure that the POST arrays contain values, that a POST method is used for the form and matching named attributes for the inputs.
FYI: Forms default to a GET method if not explicity instructed.
Note: <input type = "text" name = "var"> - $_POST['var'] match. $_POST['Var'] no match.
POST arrays are case-sensitive.
Consult:
http://php.net/manual/en/tutorial.forms.php
Error checking references:
http://php.net/manual/en/function.error-reporting.php
http://php.net/manual/en/mysqli.error.php
http://php.net/manual/en/pdo.error-handling.php
Please note that MySQL APIs do not intermix, in case you may be visiting this Q&A and you're using mysql_ to connect with (and querying with).
You must use the same one from connecting to querying.
Consult the following about this:
Can I mix MySQL APIs in PHP?
If you are using the mysql_ API and have no choice to work with it, then consult the following Q&A on Stack:
MySql php: check if Row exists
The mysql_* functions are deprecated and will be removed from future PHP releases.
It's time to step into the 21st century.
You can also add a UNIQUE constraint to (a) row(s).
References:
http://dev.mysql.com/doc/refman/5.7/en/constraint-primary-key.html
http://dev.mysql.com/doc/refman/5.7/en/alter-table.html
How to check if a value already exists to avoid duplicates?
How add unique key to existing table (with non uniques rows)

Answer 2

You have to execute your query and add single quote to $email in the query beacuse it's a string, and remove the is_resource($query) $query is a string, the $result will be the resource
$query = "SELECT `email` FROM `tblUser` WHERE `email` = '$email'";
$result = mysqli_query($link,$query); //$link is the connection
if(mysqli_num_rows($result) > 0 ){....}
UPDATE
Base in your edit just change:
if(is_resource($query) && mysqli_num_rows($query) > 0 ){
$query = mysqli_fetch_assoc($query);
echo $email . " email exists " . $query["email"] . "\n";
By
if(is_resource($result) && mysqli_num_rows($result) == 1 ){
$row = mysqli_fetch_assoc($result);
echo $email . " email exists " . $row["email"] . "\n";
and you will be fine
UPDATE 2
A better way should be have a Store Procedure that execute the following SQL passing the Email as Parameter
SELECT IF( EXISTS (
SELECT *
FROM `Table`
WHERE `email` = #Email)
, 1, 0) as `Exist`
and retrieve the value in php
Pseudocodigo:
$query = Call MYSQL_SP($EMAIL);
$result = mysqli_query($conn,$query);
$row = mysqli_fetch_array($result)
$exist = ($row['Exist']==1)? 'the email exist' : 'the email doesnt exist';

Answer 3

There are multiple ways to check if a value exists in the database. Let me demonstrate how this can be done properly with PDO and mysqli.
PDO
PDO is the simpler option. To find out whether a value exists in the database you can use prepared statement and fetchColumn(). There is no need to fetch any data so we will only fetch 1 if the value exists.
<?php
// Connection code.
$options = [
\PDO::ATTR_ERRMODE => \PDO::ERRMODE_EXCEPTION,
\PDO::ATTR_EMULATE_PREPARES => false,
];
$pdo = new \PDO('mysql:host=localhost;port=3306;dbname=test;charset=utf8mb4', 'testuser', 'password', $options);
// Prepared statement
$stmt = $pdo->prepare('SELECT 1 FROM tblUser WHERE email=?');
$stmt->execute([$_POST['email']]);
$exists = $stmt->fetchColumn(); // either 1 or null
if ($exists) {
echo 'Email exists in the database.';
} else {
// email doesn't exist yet
}
For more examples see: How to check if email exists in the database?
MySQLi
As always mysqli is a little more cumbersome and more restricted, but we can follow a similar approach with prepared statement.
<?php
// Connection code
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$mysqli = new \mysqli('localhost', 'testuser', 'password', 'test');
$mysqli->set_charset('utf8mb4');
// Prepared statement
$stmt = $mysqli->prepare('SELECT 1 FROM tblUser WHERE email=?');
$stmt->bind_param('s', $_POST['email']);
$stmt->execute();
$exists = (bool) $stmt->get_result()->fetch_row(); // Get the first row from result and cast to boolean
if ($exists) {
echo 'Email exists in the database.';
} else {
// email doesn't exist yet
}
Instead of casting the result row(which might not even exist) to boolean, you can also fetch COUNT(1) and read the first item from the first row using fetch_row()[0]
For more examples see: How to check whether a value exists in a database using mysqli prepared statements
Minor remarks
If someone suggests you to use mysqli_num_rows(), don't listen to them. This is a very bad approach and could lead to performance issues if misused.
Don't use real_escape_string(). This is not meant to be used as a protection against SQL injection. If you use prepared statements correctly you don't need to worry about any escaping.
If you want to check if a row exists in the database before you try to insert a new one, then it is better not to use this approach. It is better to create a unique key in the database and let it throw an exception if a duplicate value exists.

Answer 4

After validation and before INSERT check if username already exists, using mysqli(procedural). This works:
//check if username already exists
include 'phpscript/connect.php'; //connect to your database
$sql = "SELECT username FROM users WHERE username = '$username'";
$result = $conn->query($sql);
if($result->num_rows > 0) {
$usernameErr = "username already taken"; //takes'em back to form
} else { // go on to INSERT new record