data integrity and inserts - Mailing list pgsql-general

I want to ensure data integrity when inserting into a table, preventing
multiple
entries of identical rows of data.

Does this call for using a trigger?
How would triggers perform a query to test if data already exists in
the table?

(The doco outlines how triggers perform tests on NEW data inserted into
a
table; but I haven't found anything on data already extant.)

Thanks in advance!
Scott


sample table:

CREATE TABLE names (the_id SERIAL PRIMARY KEY, the_name text);