MSSQL RANK function is used to rank the repeating values in a manner such that similar values are ranked the same. In other words, rank function returns the rank of each row within the partition of a result set. The rank of a row is one plus the number of ranks that come before the row in question.

PARTITION BY CLAUSE

It is a same as a group by clause. Partition by clause is use for display the data in group format. Partition by clause is use only when we use the windows function otherwise we use the group by clause.

OVER CLAUSE

OVER clause defines a window or user-specified set of rows within a query result set. A window function then computes a value for each row in the window. You can use the OVER clause with functions to compute aggregated values such as moving averages, cumulative aggregates, running totals, or a top N per group results.