Window functions
A window calculation can summarize a related set of rows while keeping the original row-level detail.
OVER
Adding OVER to an eligible aggregate or window function makes it a window expression. SUM(sales) OVER () repeats the full-table sum beside every order, rather than collapsing orders into one row.
PARTITION BY
A partition divides rows into independent calculation groups. SUM(sales) OVER (PARTITION BY customer_id) repeats each customer’s total beside that customer’s orders.
Window ordering
ORDER BY inside OVER controls the calculation’s sequence. It does not guarantee the final display order; use an outer ORDER BY when the output sequence matters.
Filtering window results
In SQLite, window functions are evaluated after WHERE. Put the calculation in a CTE or derived table and filter it in an outer query. Some systems have QUALIFY; the practice engine does not.