MySQL error because of syntax in Custom PHP code - php

Question

I am trying to enter user's data into a database. I think the commas in the address are causing the error.
<?php
$full_name = $_POST["fullname"];
$email = $_POST["email"];
$password = $_POST["password"];
$full_address = $_POST["address"];
$city = $_POST["city"];
$age = $_POST["age"];
$contact_number = $_POST["number"];
$gender = $_POST["gender"];
$education = $_POST["education"];
?>
<?php
$servername = "hidden";
$username = "hidden";
$password = "hidden";
$dbname = "hidden";
// Create connection
$conn = mysqli_connect($servername, $username, $password, $dbname);
// Check connection
if (!$conn) {
die("Connection failed: " . mysqli_connect_error());
}
$sql = "INSERT INTO users (full_name, email, password,full_address,city,age,contact_number,gender,education)
VALUES ($full_name, $email, $password,$full_address,$city,$age,$contact_number,$gender,$education)";
if (mysqli_query($conn, $sql)) {
echo "New record created successfully";
} else {
echo "Error: " . $sql . "<br>" . mysqli_error($conn);
}
mysqli_close($conn);
?>

Answer 1

As others have noted, your code is vulnerable to SQL injections. You should consider using parameterized queries:
$sql = "INSERT INTO users (full_name, email, password, full_address, city, age, contact_number, gender, education)
VALUES (?,?,?,?,?,?,?,?,?)";
$stmt = mysqli_prepare($conn, $sql);
// Bind parameters
$stmt->bind_param("s", $full_name);
$stmt->bind_param("s", $email);
$stmt->bind_param("s", $password);
$stmt->bind_param("s", $full_address);
$stmt->bind_param("s", $city);
$stmt->bind_param("s", $age);
$stmt->bind_param("s", $contact_number);
$stmt->bind_param("s", $gender);
$stmt->bind_param("s", $education);
if ($stmt->execute()) {
echo "New record created successfully";
} else {
echo "Error: " . $sql . "<br>" . mysqli_error($conn);
}
For more information refer to the PHP manual on MySQLi prepared statements.

Answer 2

You need to quote string in your SQL statement;
$sql = "INSERT INTO users (full_name, email, password,full_address,city,age,contact_number,gender,education)
VALUES ('$full_name', '$email', '$password','$full_address','$city',$age,'$contact_number','$gender','$education')";
Notice the single quotes around all the variables that contain strings. I might be a bit off because I don't know the values or table structure.
But the just quote all values that are going in to a Date or Text field.
To avoid additional problems and security risks you should be using mysqli_real_escape_string (at a minimum).
In all your assignment statements wrap the values in mysqli_real_escape_string
$full_name = mysqli_real_escape_string($conn, $_POST["fullname"]);
$email = mysqli_real_escape_string($conn, $_POST["email"]);
...
Note this requires setting up your DB connection before the variable assignments, so you'll have to reorganize your code a bit.
rink.attendant.6's answer is the proper way to adapt your code.