Add column id to an existing table - php

Question

I a trying to add column id which will be a primary key with auto increment properties. So i execute this SQL query:
ALTER TABLE `user_info` ADD `id` INT NULL AUTO_INCREMENT PRIMARY KEY FIRST ;
The column is created successfully and even creates id for the already existing data.
But i am unable to insert anything inside the table anymore.
<?php
require "init.php";
$name=$_POST["user"];
$user_email=$_POST["user_email"];
$user_pass=$_POST["user_pass"];
$sql_query="SELECT * FROM user_info WHERE user_email='$user_email'";
$check=mysqli_fetch_array(mysqli_query($con,$sql_query));
if(isset($check)){
$response["success"]=false;
$response["message"]="Email already exists";
echo json_encode($response);
}else{
$sql_query="insert into user_info values('$name','$user_email','$user_pass');";
if(mysqli_query($con,$sql_query)){
//echo "<h3> Data Insert success</h3>";
$response["success"]=true;
$response["message"]="Registration successful";
echo json_encode($response);
}
else{
$response["success"]=false;
$response["message"]="Registration unsuccessful";
echo json_encode($response);
}
}
?>
I googled around and found out that i could insert 0 or null in place of my id.
I purposefully read that :
In order to take advantage of the auto-incrementing capability of the column, do not supply a value for that column when inserting rows. The database will supply a value for you.
The code works well when i drop column id but when i add it, i get response as Registration unsuccessful within my json.
The workarounds from here or here did not seem to solve my problem.
What am i missing?

Answer 1

You have four columns in your table now, however you only provide three values. Checking mysqli_error would give you an error message telling you this.
You can either change your SQL to send NULL for the id which will create an appropriate id:
insert into user_info values(null, 'Foo','Foo#example.com','password');
Or, even better is to tell MySQL which columns you are targeting. This means in the future that if you add columns your SQL wont break:
insert into user_info (name,email, password)
values('Foo','Foo#example.com','password');
Note: There is some issues with your code. You are vulnerable to SQL injection - if someone sends a malicious value it could run SQL commands you don't intend.
Additionally storing passwords in plain text is not a good idea. You should be hashing them with a secure algorithm. See: http://php.net/manual/en/faq.passwords.php

Answer 2

Your INSERT syntax was correct before you added an ID column on first place:
$sql_query="insert into user_info values('$name','$user_email','$user_pass');";
But now you should specify the columns prior to the VALUES :
$sql_query="insert into user_info (name,email, password) values('$name','$user_email','$user_pass');";