I have... (sample values)

@somevalue =3214

col1(what) col2(value) col3(valbefore)
positive 110 null
negative 232 null
positive 157 null
positive 754 null
negative 213 null


...and need to get
col1(what) col2(value) col3(valebefore)
positive 110 3324
positive 157 3481
positive 754 4235
negative 232 4003
negative 213 3790

In short, I need to update based on a previous record on a sorted table with first value acquired before