What is the correct syntax for INSERT INTO ... ON DUPLICATE KEY UPDATE in MySQL?

Question

my table(s) structure (MySQL / each one is same as below)

+-------+--------------+------+------+-------------------+
| Field | Type         | Null | Key  | Default           |
+-------+--------------+------+------+-------------------+
| id    | int(11)      | NO   | PRI  | AUTO INCREMENT    | 
| lesson| varchar(255) | NO   |      | LESSON_NAME       | 
| exam  | char(50)     | NO   |UNIQUE| NO DEFAULT        |
| quest | text         | NO   |      | NO DEFAULT        |
| answer| text         | NO   |      | NO DEFAULT        |
| note  | text         | NO   |      | NO DEFAULT        |
+-------+--------------+------+------+-------------------+

and i'am posting some values to add this table via ajax ($post) - PHP 5.0
in database.php there is a function to get posted data and add to table

function update_table ($proper_table, $name, $question, $answer, $note) {
$sql = "INSERT INTO $proper_table (id, lesson, exam, quest, answer, note) VALUES ('', '', $name, $question,$answer,$note) ON DUPLICATE KEY UPDATE exam = $name, quest = $question, answer = $answer, note = $note";
$result= mysql_query($sql)or die(mysql_error());
}

$proper_table variable is taken by another variable to add this record to correct table.
(NOTE: Original table fields and variables are different (Turkish), to be more understandable i traslated to english but the syntax is the same as you see.)
Question : I want to check that if there is a record that exam field is same then all these variables will be used for updating this record, otherwise let function put this record to proper table as a new record.
But i'am getting error like below

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 

is there any faulty coding? and what can be the solution?
Thanks right now...

Answer 1

function update_table ($proper_table, $name, $question, $answer, $note) {
    $sql = "INSERT INTO $proper_table (lesson, exam, quest, answer, note) VALUES ('', '$name', '$question','$answer','$note') ON DUPLICATE KEY UPDATE quest = VALUES(quest), answer = VALUES(answer), note = VALUES(note)";
   $result= mysql_query($sql)or die(mysql_error());
}

Just breaking this out I'll detail the changes

$sql = "INSERT INTO $proper_table 

// Removed the PK (primary key) AI (auto increment) field - don't need to specify this
(lesson, exam, quest, answer, note)     

// Likewise removed PK field, and added quotes around the text fields
VALUES ('', '$name', '$question','$answer','$note')    
ON DUPLICATE KEY UPDATE 

// If you specify VALUES(fieldName) it will update with the value you specified for the field in the conflicting row
// Also removed the exam update, as exam is the UNIQUE key which could cause conflicts so updating that would have no effect
quest = VALUES(quest), answer = VALUES(answer), note = VALUES(note)";