CREATE TABLE sampledata15 (sample_pk DECIMAL, state TEXT, year TEXT, month TEXT, day TEXT, site TEXT, commod TEXT, source_id TEXT, variety TEXT, origin TEXT, country TEXT, disttype TEXT, commtype TEXT, claim TEXT, quantity DECIMAL, growst TEXT, packst TEXT, distst TEXT)
CREATE TABLE resultsdata15 (sample_pk DECIMAL, commod TEXT, commtype TEXT, lab TEXT, pestcode TEXT, testclass TEXT, concen DECIMAL, lod DECIMAL, conunit TEXT, confmethod TEXT, confmethod2 TEXT, annotate TEXT, quantitate TEXT, mean TEXT, extract TEXT, determin TEXT)

which pesticides have been used the least?
SELECT pestcode FROM resultsdata15 GROUP BY pestcode ORDER BY COUNT(*) LIMIT 1
SELECT "pestcode" FROM "resultsdata15" GROUP BY "pestcode" ORDER BY COUNT(*) NULLS FIRST LIMIT 1