Indexing Timestamp Data

How to index a timestamp data in a Postgres table?

For example, I tried: CREATE UNIQUE INDEX idx ON table_01 (xtime);
The resulting message was: "CAN'T FIND A DEFAULT OPERATOR CLASS FOR TYPE
1296".

The table 'table_01' was created with the following command:
CREATE TABLE table_01 (
xtime TIMESTAMP,
code CHAR(5),
qty INTEGER);

The key of this table must be the 'xtime' field which is of TIMESTAMP data
type. How to do it?

Romualdo.

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