Avoiding Duplicate Records on MySQL Insert

I am having a problem trying to avoid duplicate records on my MySQL
database's primary/unique key.



If I have a database named "DB1" with a primary key value named "ID1"
(which is also the index).



And then I attempt to insert a second record to the database that has a
duplicate ID1 value of "A"



I keep getting an error.



This is the PHP statement:



$keyvalue="A";



$query = "INSERT INTO DB1 (ID1) VALUES( '$keyvalue') ON DUPLICATE UPDATE
ID1=VALUES('$keyvalue')";



$result = mysqli_query($cxn, $query)

or die("Unable to insert record into DB1: \n"."ID1:
".$keyvalue." My sql error was: ".mysqli_error($cxn));



This returns the error:



Unable to insert record into DB1: ID1: A My sql error was: 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 'UPDATE ID1=VALUES('A')' at
line 1









I also tried:



$query = "INSERT IGNORE INTO DB1 (ID1) VALUES( '$keyvalue') ";





And that did not generate an error but it did allow the duplicate value into
the table.



What am I missing here? It seems like such an easy thing to accomplish
(and with a DB2/400 table and RPG it would be!).



Thanks!


Shannon O'Donnell