window function

SQL Window Functions

1. row_number()

•Business Use Case – We want to isolate only rows for employees with the their most recent salaries

•Could be still active employees, i.e. to_date = ‘9999-01-01’ or employees who have left the company**, what was their salary when they left?

2. lead/lag

1. lead ———take value from row below

1） wrong ex：

2） correct ex：

1. lag ———take value from row above

3. cumulative sum