php mysql insert query having trouble - php

Question

I have a query which is not inserting if i use the where clause, without the where clause it inserts data. this is weird and I have never seen it happen before in WAMP
$key=substr(md5(rand(0, 1000000)), 0, 5);
$key1="INSERT INTO login(key_id) VALUES('$key')
WHERE (email_id = '" . mysql_real_escape_string($_POST['email_id']) . "')"
if(mysql_query($key1))
{
$message = 'User Added!.';
echo "<SCRIPT>
alert('$message');
location='forgotpassword.php';
</SCRIPT>";
}
If I echo $_POST['email_id'] it does return valid result

Answer 1

INSERT and WHERE do not mix.
when INSERTing, you are creating a new record.
WHERE is used with SELECTing DELETEing or UPDATEing, when you have to specify a filter which rows you want to SELECT, DELETE or UPDATE.
if you want to INSERT a row, do not use WHERE.
if you want to change a row, use
$key1="UPDATE login SET key_id = '$key' WHERE
(email_id = '" . mysql_real_escape_string($_POST['email_id']) . "')";

Answer 2

Insert is only used on creating new record and where clause is only used if want to set any condition it is used with like select,update,delete.
Try this it will help:-
$key1="update login set key_id ='$key' WHERE
(email_id = '" . mysql_real_escape_string($_POST['email_id']) . "')";

Answer 3

I know #Franz-Gleichmann is already explained very well, whats wrong in your code.
You need to use UPDATE for updating data modified code:
$key1 = "UPDATE login SET key_id = '$key' WHERE
(email_id = '" . mysql_real_escape_string($_POST['email_id']) . "')";
Now i am adding two more points:
Please use mysqli_* or PDO, because mysql_* is deprecated and not available in PHP 7.
You missed the termination semi colon on the same line, i hope this is typo error.