The frame determines which rows are included in the calculation for the current input row, based on their relative position to the current row.
If you use an aggregate function instead of LEAD or LAG, you must specify a window frame. LEAD and LAG reference individual row sand ignore the frame specification.
The start offset and end offset describe the number of rows that appear before and after the current input row. An offset of "0" represents the current input row. For example, a start offset of -3 and an end offset of 0 describes a frame including the current input row and the three rows before the current row.
The following image shows a frame with a start offset of -1 and an end offset of 1:
For every input row, the function performs an aggregate operation on the rows inside the frame. If you configure an aggregate expression like SUM with the preceding frame, the expression calculates the sum of the values within the frame and returns a value of 6000 for the input row.
You can also specify a frame that does not include the current input row. For example, a start offset of 10 and an end offset of 15 describes a frame that includes six total rows, from the tenth to the fifteenth row after the current row.
The start offset must be less than or equal to the end offset.
All Rows Preceding
All Rows Following
represent the first row of the partition and the last row of the partition. For example, if the start offset is All Rows Preceding and the end offset is -1, the frame includes one row before the current row and all rows before that.