  The decreasing norm-trace codes are evaluation codes defined by a set of
monomials closed under divisibility and the rational points of the extended
norm-trace curve. In particular, the decreasing norm-trace codes contain the
one-point algebraic geometry (AG) codes over the extended norm-trace curve. We
use Gr\"obner basis theory and find the indicator functions on the rational
points of the curve to determine the basic parameters of the decreasing
norm-trace codes: length, dimension, and minimum distance. We also obtain their
dual codes. We give conditions for a decreasing norm-trace code to be a
self-orthogonal or a self-dual code. We provide a linear exact repair scheme to
correct single erasures for decreasing norm-trace codes, which applies to
higher rate codes than the scheme developed by Jin, Luo, and Xing (IEEE
Transactions on Information Theory {\bf 64} (2), 900-908, 2018) when applied to
the one-point AG codes over the extended norm-trace curve.
