SUM() OVER()

What is SUM() OVER()?

SUM() OVER() is a window function that calculates a sum across a set of rows without collapsing the result. It lets you see individual row values alongside cumulative or partitioned totals.

Syntax

-- Total sum across all rows
SELECT col, SUM(col) OVER () AS total_sum FROM table_name;

-- Running total
SELECT col, SUM(col) OVER (ORDER BY date_col) AS running_total FROM table_name;

-- Sum per partition
SELECT col, SUM(col) OVER (PARTITION BY group_col) AS group_sum FROM table_name;

When to Use

• Showing each row with its percentage of the total
• Computing running totals (cumulative sums)
• Comparing individual values to group totals

Key Points

1. Empty OVER() — SUM() OVER() computes the total across all rows, repeated on every row.
2. Running Total — SUM() OVER(ORDER BY col) computes a cumulative sum.
3. Partitioned Sum — SUM() OVER(PARTITION BY col) computes a sum per group.
4. Percentage — Compute percentage: col / SUM(col) OVER() * 100.
5. No Collapsing — Unlike GROUP BY, every row remains visible.