How to fix ER_WINDOW_NO_CHILD_PARTITIONING (3581): Child window cannot have PARTITION BY in MySQL

Look for your WINDOW clause where the named window has a PARTITION BY clause. Find where you reference this window in an OVER clause and attempt to add another PARTITION BY.

-- Problem example
WINDOW w AS (PARTITION BY region)
-- Then later trying to use:
OVER (w PARTITION BY category)  -- This causes error 3581

Simply remove the PARTITION BY clause from the OVER clause that references the named window. The OVER clause will inherit the partitioning from the named window definition.

-- Correct usage
WINDOW w AS (PARTITION BY region)
-- Use it without additional PARTITION BY:
SUM(amount) OVER (w ORDER BY date)

Instead of trying to modify a named window, define multiple named windows with different partitioning strategies. This is the recommended approach when you need the same window function calculated with different partition schemes.

WINDOW 
  w_by_region AS (PARTITION BY region),
  w_by_category AS (PARTITION BY category)
SELECT
  SUM(amount) OVER (w_by_region ORDER BY date) AS region_sum,
  SUM(amount) OVER (w_by_category ORDER BY date) AS category_sum
FROM sales

For complex cases where you need fine-grained control over partitioning, define window specifications directly in the OVER clause rather than referencing named windows.

SELECT
  SUM(amount) OVER (PARTITION BY region ORDER BY date) AS region_sum,
  SUM(amount) OVER (PARTITION BY category ORDER BY date) AS category_sum
FROM sales

Execute your corrected query to confirm the error is resolved. Check that the window function calculations are producing the expected results with the correct partitioning.