What is the purpose of the RANK function in SQL?

The RANK function in SQL is used to assign a unique rank to each distinct row within a result set.

The RANK function is a window function in SQL that provides a unique rank to each row within a partition of a result set. It is particularly useful when you want to find the relative ranking of rows in a result set. The function assigns a unique rank number to each distinct row, with the same rank for duplicate values. However, if there is a tie for a position, the RANK function will skip the next rank(s).

For example, if you have a table of students with their scores in a test, you can use the RANK function to assign a rank to each student based on their score. If two students have the same score, they will receive the same rank, and the next score will be assigned the rank that would have been next if there were no tie.

The syntax for the RANK function is: RANK() OVER ( [ partition_by_clause ] order_by_clause ). The partition_by_clause divides the result set produced by the FROM clause into partitions to which the RANK function is applied. If you omit it, the function treats the whole result set as a single partition. The order_by_clause determines the order of the data in each partition. The first row in each partition is given a rank of 1.

The RANK function is a very useful tool in SQL, especially when dealing with large datasets where manual ranking would be impractical. It allows for easy identification of highest or lowest values, and can be used in conjunction with other SQL functions to create more complex queries and analyses.