Over command

A window function in SQL:2003 is an aggregate function applied to a partition of the result set.
For example, sum(population) OVER( PARTITION BY city )
calculates the sum of the populations of all rows having the same city value as the current row.
Partitions are specified using the OVER clause which modifies the aggregate. Syntax: :: =
OVER ( [ PARTITION BY , ... ]
[ ORDER BY ] )
The OVER clause can partition and order the result set. Ordering is used for order-relative functions such as row_number.