What is rows unbounded preceding used for in teradata?

@denis 

In Teradata, the clause 'ROWS UNBOUNDED PRECEDING' is used in window functions to define a window frame that starts from the first row of the partition and includes all rows up to and including the current row. This means that the window frame will include all rows from the beginning of the partition up to the current row.

This clause allows you to calculate aggregates or perform other calculations on a specific range of rows within a partition in a window function. By using 'ROWS UNBOUNDED PRECEDING', you can include all rows from the start of the partition up to the current row in the calculation.