add mysql row if userID do not exist in table - php

Question

i'm sending a post request to this code:
$name = (string)$_POST['name'];
$id = (int)$_POST['id'];
$query = "INSERT INTO Users (name, userID) VALUES ('$name', '$id')";
$result = mysqli_query($link,$query);
Which works fine and it adds a row to the table. How do i check wether the userID all ready exist in one of the following rows?

Answer 1

Do it like this
$query = "SELECT COUNT(*) FROM Users WHERE userID = '$id'";
$result = mysqli_query($link,$query);
if ( mysqli_fetch_assoc($result) ) {
$message = "Already exists";
} else {
$query = "INSERT INTO Users (name, userID) VALUES ('$name', '$id')";
$result = mysqli_query($link,$query);
}

Answer 2

Try this
$name = (string)$_POST['name'];
$id = (int)$_POST['id'];
$res = mysqli_query($link, "SELECT * FROM Users WHERE userID = '$id' LIMIT 1 ");
if($row = mysqli_fetch_assoc($res))
{
echo "this user id is already exists";
}
else
{
$query = "INSERT INTO Users (name, userID) VALUES ('$name', '$id')";
$result = mysqli_query($link,$query);
echo "record inserted successfully ";
}
REMEMBER : always use LIMIT 1 when you trying to get exactly one result.

Answer 3

IF you have properly set 'id' as primary key or unique key in your table, you can use the modifier IGNORE in your query you don't get an error when you try to isert a duplicate.
Doing this will result in the row only being inserted if the value of the primary key wasn't already in the table.
$query = "INSERT IGNORE INTO Users (name, userID) VALUES ('$name', '$id')";
IF you haven't set a primary key in your table you will have to do a SELECT query to find out if a row with that id is already in your table.

Answer 4

Make the UserID an Unique Key.
If it already exists, your code will throw an error and the row will not be insterted.
alter table Users
add unique index Unique_user (userID (8000))

Answer 5

Before inserting the values to the table check whether the following user id exists in the table or not
You can do it in this way
$name = $_POST['name'];
$id = $_POST['id'];
$sql = "SELECT * FROM Users WHERE userID = '$id'";
$res= mysqli_query($sql);
$num = mysqli_num_rows($res);
if($num == 0)
{
$query2 = "INSERT INTO Users (name, userID) VALUES ('$name', '$id')";
$result2 = mysqli_query($query2);
echo "record inserted successfully ";
}
else
{
echo "Record Failed !!";
}