Capture specific values from SQL query using PHP

so I'm new to PHP, and I wanna understand the basic server authentication process for a web login form.

1. User types in details into the input elements
2. Javascript to validate content typed in
3. Here is where it gets blurry - PHP takes the value of the input fields, and checks if there's a similar username in the DB...
4. If there is, then it compares the passwords, and if there's a match, proceed, otherwise trigger a javascript function to show 'wrong credentials' to the user

Now, for step 3:

I know I need to use PHP to execute a SQL query that goes like:

SELECT * FROM users WHERE user_name like $input开发者_如何学Go_user

But what do you do about this? I seem to not understand the basics here, I think I need a tutorial. :-(

You need to authenticate the user with his username and password.

$result = mysql_query("SELECT * FROM users WHERE username='$username' and passwoed='$password'");

$fetch = mysql_array_fetch($result);

if(mysql_num_rows($result)==1) {
$_SESSION["member_id"] = $fetch["id"];
}

Now the $_SESSION["member_id"] is available in all your pages. Look at the below link on more information about this.

http://www.tutorialized.com/tutorial/Create-a-Log-in-out-System-or-Script-for-a-Webpage.-UPDATED/69498

http://www.codewalkers.com/c/a/Miscellaneous/Writing-a-Basic-Authentication-System-in-PHP/

Of course you coulda easily googled this out!

I hope this can help you about checking the username :

$query=mysql_query("SELECT * FROM user WHERE username='$username' AND password='$password'");
$query=mysql_num_rows($query);
if($query==0) { echo "Wrong username or password."; }
else { //do what you want }

And you can search some tutorial from http://www.w3schools.com/ or http://www.google.com