Window functions in MySQL cannot have ORDER BY redefined when the named window already contains an ORDER BY clause. Remove the redundant ORDER BY from the OVER clause to resolve this error.
MySQL window functions use named windows to define partitioning and ordering behavior. When you reference a named window in an OVER clause, you cannot add or modify properties that already exist in the window definition. This error specifically occurs when you try to specify an ORDER BY clause in the OVER clause when the referenced named window already has its own ORDER BY clause. MySQL treats this as an attempt to redefine the window, which is not allowed. The two ORDER BY clauses conflict—one in the OVER clause and one in the WINDOW definition—and MySQL cannot determine which should take precedence.
Look for your window function query and locate where ORDER BY appears twice: once in the OVER clause and once in the WINDOW definition.
SELECT District, Name, Population,
SUM(Population) OVER(wf ORDER BY Name) -- ORDER BY #1 (in OVER)
FROM City
WHERE CountryCode = 'AUS'
WINDOW wf AS (PARTITION BY District ORDER BY Name); -- ORDER BY #2 (in WINDOW)This query has ORDER BY in both places, which causes the error.
The safest fix is to remove the ORDER BY from the OVER clause, since the named window already defines the ordering:
SELECT District, Name, Population,
SUM(Population) OVER(wf) -- Remove ORDER BY here
FROM City
WHERE CountryCode = 'AUS'
WINDOW wf AS (PARTITION BY District ORDER BY Name); -- Keep ORDER BY in definitionThis allows the window function to use the ordering defined in the named window without conflict.
If you need different ordering for different aggregate functions, define the base window without ORDER BY, then add it only where needed:
SELECT District, Name, Population,
SUM(Population) OVER(wf ORDER BY Name) AS cumulative_sum,
COUNT(*) OVER(wf) AS total_count
FROM City
WHERE CountryCode = 'AUS'
WINDOW wf AS (PARTITION BY District); -- No ORDER BY in definitionThis works because you're only adding ORDER BY where it's not already defined, not redefining it.
Execute your modified query to verify it runs without error:
SELECT District, Name, Population,
SUM(Population) OVER(wf) as cumulative_sum,
ROW_NUMBER() OVER(wf) as row_num
FROM City
WHERE CountryCode = 'AUS'
WINDOW wf AS (PARTITION BY District ORDER BY Population DESC);If the query executes successfully and returns expected results, the error is resolved.
Window inheritance in MySQL is strict: once a named window is defined with PARTITION BY, ORDER BY, or frame specifications, you cannot override those same properties in the OVER clause. You can only extend a named window by adding properties that weren't in the original definition. For example, if a window has PARTITION BY but no ORDER BY, you can add ORDER BY in the OVER clause. However, if it already has ORDER BY, you cannot change or redefine it. This design prevents ambiguity in window function semantics. When working with complex queries that need multiple different window orderings, use CTEs (WITH clauses) to define intermediate result sets, each with its own window function, rather than trying to modify windows.
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