CREATE INDEX question (how to index on "money" field?)

QUICK VERSION: How do I create an index on a field of type "MONEY"?

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LONG VERSION:

I have a table with a field of type "money". I very often need to
access records by the purchase price so I thought I'd create an index
to help out my selects:

CREATE INDEX purchasepriceidx ON mytable (purchaseprice);

This results in the following:

ERROR: data type money has no default operator class for access
method "btree" You must specify an operator class for the
index or define a default operator class for the data type

So if I understand this message correctly, it means that "money" has
no comparison operators associated with it? I RTFM'd and found the 51
available operators (SELECT am.amname AS acc_method, opc.opcname AS
ops_name FROM pg_am am, pg_opclass opc WHERE opc.opcamid = am.oid
ORDER BY acc_method, ops_name), but I don't see anything here that
seems to relate to "money" type fields. Am I correct about my
assuptions? Anyone have suggestions they can share? Any simple
examples posted anywhere?

PostgreSQL 7.3.4 on i586-pc-linux-gnu, compiled by GCC 2.96

Thanks,

Stephane Charette
stephanecharette @@@ telus ... net