Sintáxis:
CREATE AGGREGATE agg_name [AS] (BASETYPE = data_type,
[SFUNC1 = sfunc_1, STYPE1 = sfunc1_return_type]
[SFUNC2 = sfunc_2, STYPE2 = sfunc2_return_type]
[,FINALFUNC = final-function]
[,INITCOND1 = initial-cond1][,INITCOND2 = initial-cond2]);