Excellent!! That's all we wanted to teach you today. Let's review what we've learned:

• LEAD(x) and LAG(x) give you the next/previous value in the column x, respectively.
• LEAD(x,y) and LAG(x,y) give you the value in the column x of the row which is y rows after/before the current row, respectively.
• FIRST_VALUE(x) and LAST_VALUE(x) give you the first and last value in the column x, respectively.
• NTH_VALUE(x,n) gives you the value in the column x of the n-th row.
• LAST_VALUE and NTH_VALUE usually require the window frame to be set to

  ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING

Now, are you ready for a short quiz?