Adding Window Functions to a Spreadsheet

Traditional spreadsheets like Excel struggle with running totals because formulas reference cells by position rather than logical relationships—inserting or deleting rows breaks calculations without warning. SQL window functions like LAG() and LEAD() solve this problem for developers, but remain too complex for typical spreadsheet users. Grist addresses this by introducing a PREVIOUS() function that references the actual previous record by date rather than cell position, automatically maintaining correct calculations even when rows are rearranged.