You have to do this with two queries, first issue a select to see if the value exists. Then, if the value does not exist (via Perl's if or unless), insert it with the second query.

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)