concatenate mysql select query with php variable? - php

Question

I am trying to concatenate a MySQL SELECT query with PHP variable but got an error.
My PHP statement which gives an error is:
$result=mysql_query("SELECT user_id,username,add FROM users WHERE username =".$user."AND password=".$add);
and error as:
( ! ) Notice: Undefined variable: info in C:\wamp\www\pollBook\poll\login.php on line 18
Call Stack
I don't understand where I missed the code.
When I write query without WHERE clause it works fine.

Answer 1

The reason why your code isn't working
You are attempting to use a variable, $info, that has not been defined. When you attempt to use an undefined variable, you're effectively concatenating nothing into a string, however because PHP is loosely typed, it declares the variable the second you reference it. That is why you're seeing a notice and not a fatal error. You should go through your code, and ensure that $info gets a value assigned to it, and that it is not overwritten at some point by another function. However, more importantly, read below.
Stop what you are doing
This is vulnerable to a type of attack called an SQL Injection. I'm not going to tell you how to concatenate SQL strings. It's terrible practice.
You should NOT be using mysql functions in PHP. They are deprecated. Instead use the PHP PDO Object, with prepared statements. Here's a rather good tutorial.
Example
After you've read this tutorial, you'll be able to make a PDO Object, so I'll leave that bit for you.
The next stage is to add your query, using the prepare method:
$PDO->prepare("SELECT * FROM tbl WHERE `id` = :id");
// Loads up the SQL statement. Notice the :id bit.
$actualID = "this is an ID";
$PDO->bindParam(':id', $actualID);
// Bind the value to the parameter in the SQL String.
$PDO->execute();
// This will run the SQL Query for you.

Answer 2

You are missing space before "AND " and you should use single quotes as suggested in other answers.
$result=mysql_query("SELECT user_id,username,add FROM users WHERE *username =".$user."AND* password=".$add);
Updated:
echo $sql = "SELECT user_id,username,add FROM users WHERE username ='".$user."' AND password='".$add."'";
$result=mysql_query($sql);

Answer 3

although there is no $info variable used in the query but you need to correct the query:
$result=mysql_query("SELECT user_id,username,add FROM users WHERE username ='" . $user . "' AND password='" . $add . "'");

Answer 4

First from the error its looks like one of your variables is not defined. .. check it. Second surround your parameters with ' for safer syntax.

Answer 5

This is because the variables you are using might not have defined above
So first initialize your variables or if its coming from somewhere else(POST or GET) then check with isset method
So complete code would be
$user = 123; // or $user = isset($user)?$user:123;
$add = 123456; // or $add = isset($add)?$add:123456;
And then run your query
$result=mysql_query("SELECT user_id,username,add FROM users WHERE username =".$user."AND password=".$add);