ROW_NUMBER function

Window functions are used to calculate stuff about the current row.

For example What if we want to calculate all of the drinks that were bought until 1995, 1997, 1999, etc.? What if we want to find the best Olympic performer for each period (2000, 2004, 2008)?

Maybe the best performer for 2000 and 2004 is James, and for 2008 is John because he is better than James.

All of this can be solved using window functions.

The ROW_NUMBER() OVER () is numbering the rows with a specific criterion. The criterion should be inside the OVER (). If no criterion is specified then it will number the rows with the same order.

For example:

SELECT *, ROW_NUMBER() OVER () as row_num
FROM table1

This will add a column row_num that will go from 1 to n (n - number of rows)