Prepared Statements Checking if row exists - php

Question

I am new to Prepared Statements in Php and and wondering how you would best approach checking if a row already exists as I seem to be getting confused at this stage:
<?php
include '../config.php';
$stmt = $conn->prepare("INSERT INTO users (email, password) VALUES (?, ?)");
$stmt->bind_param("ss", $email, $password);
if(mysqli_num_rows($stmt) > 0) {
$email = $_POST['email'];
$password = $_POST['password'];
$stmt->execute();
header('Location: ../login.php');
} else {
echo 'user already exists';
}
$stmt->close();
$conn->close();
?>
The above returns the else statement, if I switch them around it will insert again making use of the else statement and inserting the record but still not checking.
** UPDATE **
Here is my updated code for you to see after assistance below..
<?php
include '../config.php';
ini_set('display_errors', 1); ini_set('display_startup_errors', 1); error_reporting(E_ALL);
$email = $_POST['email'];
$password = $_POST['password'];
$stmt_check = $conn->prepare("SELECT * FROM users WHERE email =?");
$stmt_check->bind_param("s", $email);
$stmt_check->execute();
if($stmt_check->num_rows > 0) {
echo 'user already exists';
} else {
$stmt = $conn->prepare("INSERT INTO users (email, password) VALUES (?, ?)");
$stmt->bind_param("ss", $email, $password);
$stmt->execute();
// header('Location: ../login.php');
}
$stmt->close();
$conn->close();
?>

Answer 1

mysqli_num_rows applicable to SELECT statement.
$stmt_check = $conn->prepare("SELECT * FROM users WHERE email =? AND password =?");
$stmt_check->bind_param("ss", $email, $password);
$stmt_check->execute();
if(mysqli_num_rows($stmt_check) > 0)
Updated Code
<?php
include '../config.php';
$email = $_POST['email'];
$password = $_POST['password'];
$stmt_check = $conn->prepare("SELECT * FROM users WHERE email =? AND password =?");
$stmt_check->bind_param("ss", $email, $password);
$stmt_check->execute();
if($stmt_check->num_rows > 0){
echo 'user already exists';
} else {
$stmt = $conn->prepare("INSERT INTO users (email, password) VALUES (?, ?)");
$stmt->bind_param("ss", $email, $password);
$stmt->execute();
header('Location: ../login.php');
}
$stmt->close();
$conn->close();
?>
Quick Link
mysqli_num_rows
mysql_num_rows
Which States,
This command is only valid for statements like SELECT or SHOW that
return an actual result set. To retrieve the number of rows affected
by a INSERT, UPDATE, REPLACE or DELETE query, use
mysql_affected_rows().
Edit 1
Change
if(mysqli_num_rows($stmt_check) > 0){
To
if($stmt_check->num_rows > 0){
See Example2 of PHP mysqli_num_rows() Function

Answer 2

This is my updated code, please try
<?php
include '../config.php';
$email = $_POST['email'];
$password = $_POST['password'];
$stmt_check = $conn->prepare("SELECT * FROM users WHERE email =? AND password =?");
$stmt_check->bind_param("ss", $email, $password);
$stmt_check->execute();
$stmt_check->store_result();
$numberofrows = $stmt_check->num_rows;
if(($numberofrows) > 0)
echo 'user already exists';
} else {
$stmt = $conn->prepare("INSERT INTO users (email, password) VALUES (?, ?)");
$stmt->bind_param("ss", $email, $password);
$stmt->execute();
header('Location: ../login.php');
}
$stmt->close();
$conn->close();
?>

Answer 3

Take a look at mysqli_stmt_affected_rows()
<?php include '../config.php';
$stmt = $conn->prepare("INSERT INTO users (email, password) VALUES (?, ?)");
$stmt->bind_param("ss", $_POST['email'], $_POST['password']);
$stmt->execute();
if(mysqli_stmt_affected_rows($stmt) > 0)
{
header('Location: ../login.php');
}
else
{
echo 'user already exists';
}
$stmt->close();
$conn->close();
?>

Answer 4

<?php include '../config.php';
$stmt = $conn->prepare("INSERT INTO users (email, password) VALUES (?, ?)");
$stmt->bind_param("ss", $_POST['email'], $_POST['password']);
$result = $stmt->execute(); // this return a bool: true if row affected otherwise false
if($result)
{
header('Location: ../login.php');
}
else
{
echo 'user already exists';
}
$stmt->close();
$conn->close();
?>