ON DUPLICATE KEY not working correctly - mysql

Question

I am running the following query, but getting an error. I think it is coming from the ON DUPLICATE KEY part, but I'm not 100% sure what the correct syntax is to use there.
<?php
$form_id = $form->data['form_id'];
$cfid = $form->data['cf_id'];
$datesent = $form->data['datesent'];
$query = mysql_query("
INSERT INTO `email_history` (
`cf_id` ,
`$form_id`
)
VALUES (
'$cfid', '$datesent'
)
ON DUPLICATE KEY
UPDATE INTO
`email_history` (
`$form_id`
)
VALUES (
'$datesent'
);
") or die(mysql_error());
?>
EDIT
Using the following I am getting this error :
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')' at line 10
<?php
$form_id = $form->data['form_id'];
$cfid = $form->data['cf_id'];
$datesent = $form->data['datesent'];
$query = mysql_query("
INSERT INTO `email_history` (
`cf_id` ,
`$form_id`
)
VALUES (
'$cfid', '$datesent'
)
ON DUPLICATE KEY
UPDATE `$form_id` = `$datesent`
);
") or die(mysql_error());
?>

Answer 1

The correct syntax of ON DUPLICATE KEY is something a long the lines described below.
Please note that it's just an example snippet, though it should be clear why your provided snippet fails to execute.
INSERT INTO tbl (
col1, col2, ... , colN
) VALUES (
#val1, #val2, ..., #valN
) ON DUPLICATE KEY UPDATE
col3 = VALUES(col3), col4 = #val4
Documentation
MySQL 5.0 Reference Manual :: 12.2.5.3 INSERT ... ON DUPLICATE KEY UPDATE Syntax
How would that look in my code?
$form_id = $form->data['form_id'];
$cfid = $form->data['cf_id'];
$datesent = $form->data['datesent'];
$query = mysql_query (<<<EOT
INSERT INTO `email_history` (`cf_id`, `$form_id`)
VALUES ('$cfid', '$datesent')
ON DUPLICATE KEY UPDATE `$form_id` = VALUES(`$form_id`)
EOT
) or die (mysql_error ());
What does VALUES($form_id) do?
It will yield the value of what was originally passed as the value for column named $form_id.
What is the use of <<<EOT?
In the previous snippet we are using a HEREDOC to have a string span multiple lines in an easy manner. You can read more about it in the documentation for heredocs.