Coding skills here for learning
unbounded preceding n, precending, n current row n, following, n Unbounded following
unbounded preceding: from begining up to the current row
n, preceding: n rows before current row
n, following: means using current row and after n rows
unbounded following: start from current row and go in the end of the partition
n, preceding: n rows before current row
n, following: means using current row and after n rows
unbounded following: start from current row and go in the end of the partition