How would I go about checking a database [with PHP] for identical information before submitting new information. I'm creating a mailing list and I want to make sure people don't submit the same email twice.

Thanks,
Micah

When registering the email, do this:

PHP Code:

$sql = "SELECT *
FROM `your_table`
WHERE `email`='".$useremail."'";
$sql = @mysql_query($sql);
if(!$sql){die("MySQL Error! ".mysql_error()); }
$sql = @mysql_fetch_array($sql);
if(!empty($sql['email'])){
  die "Error, email already in use.";
} 


Theres quite a few things you need to change there though.
- In the query, change the table name to your table name
- In the query, change the `email` column to the correct name.
- $useremail is the value of the email thats about to be submitted. This is the email that we are checking for duplicates of.
- you need to change $sql['emai'] to $sql['whatever_your_email_column_is'];.

If it doesnt work, post the SQL error or Parse error or whatever.

Thank you, AxE. I did get an error, however. You should know I'm not extremely knowledgeable about PHP, so please be patient with me. The error I received was this: "Parse error: parse error, unexpected T_CONSTANT_ENCAPSED_STRING in add.php on line 28"

Can you show us your whole script and point out line 28?

That error is usually given when you specify a variable inside a string( using the "String " . $var . "String" method) but miss a peroid off somewhere. But, Like 0beron said, can you post the whole code and point out the error line?

I'm sorry. It was kind of stupid of me to assume you could know what my problem is without looking at my code. Anyway, I changed it around some, so I have the same error, only on line 34. Here is what I did:

PHP Code:

$name = $HTTP_POST_VARS["input_name"];
$ml_email = $HTTP_POST_VARS["input_email"];

if (!eregi("^[a-zA-Z0-9_]+@[a-zA-Z0-9\-]+\.[a-zA-Z0-9\-\.]+$", $ml_email))
{
echo "That is not a valid email adress.  Please return to the previous page and try <a href=\"ml.html\">again</a>.";
exit;
} else {
mysql_connect("localhost","user","pass") or die("Error connecting to Database!<br>" . mysql_error());
mysql_select_db("rebhedge_DB1") or die("Error selecting Database!<br>" . mysql_error());

 $sql = "SELECT *
FROM `ml`
WHERE `email`='".$ml_email."'";
$sql = @mysql_query($sql);
if(!$sql){die("MySQL Error! ".mysql_error()); }
$sql = @mysql_fetch_array($sql);
if(!empty($sql['email'])){
/*Line 34*/  die "Error, email already in use.";
} 


Die is a function, try die("Error, email already in use");

Sorry about that, my bad.

Thanks, Axe. You've saved my butt in two areas of the same project. I really appreciate you taking the time to do help me out.

Sorry I seem to have run into more problems. I get the error message "Parse error: parse error, unexpected $ in add.php on line 22" when my code is this:

PHP Code:

<?php
$name = $HTTP_POST_VARS["input_name"];
$ml_email = $HTTP_POST_VARS["input_email"];

if (!eregi("^[a-zA-Z0-9_]+@[a-zA-Z0-9\-]+\.[a-zA-Z0-9\-\.]+$", $ml_email))
{
echo "That is not a valid email adress.  Please return to the previous page and try <a href=\"ml.html\">again</a>.";
exit;
} else {
mysql_connect("localhost","user","pass") or die("Error connecting to Database!<br>" . mysql_error());
mysql_select_db("rebhedge_DB1") or die("Error selecting Database!<br>" . mysql_error());

 $sql = "SELECT *
FROM `ml`
WHERE `email`='".$ml_email."'";
$sql = @mysql_query($sql);
if(!$sql){die("MySQL Error! ".mysql_error()); }
$sql = @mysql_fetch_array($sql);
if(!empty($sql['email'])){
  die("Error, email already in use");
}
/*This being Line 22*/?>

You've missed a } off the end. You have Two IF statements there, but only one closed one. Add } on to line 22

AxE, you're my hero. I really appreciate your help!

Glad I could help

Maybe it's better to desidn the DB in such a way that 'email' field is set as UNIQUE?

I would also create an index before querying a medium sized table with it.