Let's consider the bank_accounts table we have used in the previous sections:

Let's assume we want to add information to the table about which class each user belongs to based on their account balance.

The classes will be determined as follows:

• A person whose account balance is in the bottom 25% will belong to the forth class;
• A person whose account balance is between 25% and 50% will belong to the third class;
• A person whose account balance is between 50% and 75% will belong to the second class;
• A person whose account balance is in the top 25% will belong to the first class.

To solve this problem, we can use a window function called NTILE().
The NTILE() function is a window function that divides the rows in an ordered partition into a specified number of roughly equal groups, or "tiles".
It assigns each row a group number, starting at 1, based on the group it falls into.

Note

In the example, we don't need to specify a PARTITION BY clause because we want to apply the NTILE() function to the entire result set, not to specific subsets or partitions of the data.
The ORDER BY clause is sufficient as it defines the order in which the rows are distributed into tiles, ensuring that the grouping is based on the sorted order of the salaries across the entire table.
If we wanted to calculate tiles within specific groups (e.g., departments), we would use PARTITION BY.