Grouping by or iterating through partitions in SQL

Question

Two part question regarding partitioning in SQL.

In T-SQL when you use PARTITION BY is there a way to assign a unique number to each partition, in addition to something

Answer 1

You could use dense_rank():

select  *
,       row_number() over (partition by Action order by Timestamp) as RowNum
,       dense_rank() over (order by Action) as PartitionNum
from    YourTable

Example at SQL Fiddle.

T-SQL is not good at iterating, but if you really have to, check out cursors.