A useful feature would be declaration of user defined global constants at the server or database level.
DECLARE CONST @@PI NUMERIC(12,10) = 3.1415926535;
DECLARE CONST @@StatusInProcess TINYINT = 2;
DECLARE CONST @@StatusDelivered TINYINT = 3;
DECLARE CONST @@GB BIGINT = 1073741824;
You can kind of do this using scalar functions, but that can potentially have adverse effects on query execution plans.
"Do not seek to follow in the footsteps of the wise. Instead, seek what they sought." - Matsuo Basho