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Description

This error occurs in MySQL when an SQL statement attempts to define a named window more than once within the same scope. It typically arises when using `WINDOW` clauses for analytic functions, indicating that a window alias has been inadvertently reused.

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Error Message

Window '%s' is defined twice.

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Known Causes

3 known causes

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Duplicate Window Name in Query

An SQL query or view definition explicitly defines the same window name multiple times within its `WINDOW` clause.

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Copy-Paste Coding Mistakes

Code duplication through copy-pasting existing `WINDOW` clause definitions can inadvertently introduce a second, identical window name.

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Automated SQL Generation Issues

Tools or scripts that programmatically generate complex SQL queries might mistakenly produce redundant `WINDOW` clause definitions.

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Solutions

3 solutions available

1. Identify and Remove Duplicate Window Definitions easy

Locate and delete redundant 'OVER' clause definitions with the same name.

1

Examine your SQL query that is causing the error. Look for multiple `OVER` clauses that have been assigned the same alias (the '%s' in the error message).

SELECT
    column1,
    column2,
    SUM(column1) OVER my_window AS sum_col1,
    AVG(column2) OVER my_window AS avg_col2 -- This is likely the duplicate definition
FROM
    your_table;

2

Rename one of the duplicate window definitions to a unique name or remove it entirely if it's not needed.

SELECT
    column1,
    column2,
    SUM(column1) OVER my_window_sum AS sum_col1,
    AVG(column2) OVER my_window_avg AS avg_col2 -- Renamed to a unique name
FROM
    your_table;

3

Alternatively, if one of the window definitions is identical and redundant, simply remove it.

SELECT
    column1,
    column2,
    SUM(column1) OVER my_window AS sum_col1
FROM
    your_table;

2. Consolidate Window Definitions medium

Combine multiple window definitions into a single, reusable definition if they share the same parameters.

1

Identify window definitions that have identical `PARTITION BY`, `ORDER BY`, and `frame clause` specifications. These are prime candidates for consolidation.

SELECT
    column1,
    column2,
    SUM(column1) OVER (PARTITION BY category ORDER BY date ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS running_total,
    AVG(column2) OVER (PARTITION BY category ORDER BY date ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS running_avg -- Same partition and order, can be consolidated
FROM
    your_table;

2

Define a single named window with the common specifications.

SELECT
    column1,
    column2,
    SUM(column1) OVER my_common_window AS running_total,
    AVG(column2) OVER my_common_window AS running_avg
FROM
    your_table
WINDOW
    my_common_window AS (PARTITION BY category ORDER BY date ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW);

3. Review Complex CTEs and Subqueries advanced

Scrutinize Common Table Expressions (CTEs) and subqueries for accidental redefinition of window functions.

1

If your query involves CTEs or subqueries, carefully trace the flow of data and window function definitions. The error might originate from a CTE that redefines a window function already defined in the outer query or another CTE.

WITH
  cte1 AS (
    SELECT
      column1,
      SUM(column1) OVER my_window AS sum1
    FROM
      table1
  ),
  cte2 AS (
    SELECT
      column2,
      AVG(column2) OVER my_window AS avg2 -- Potential duplicate definition of 'my_window'
    FROM
      table2
  )
SELECT
  * 
FROM cte1 JOIN cte2 ON ...;

2

Ensure that window function names are unique across all levels of CTEs and subqueries, or use the `WINDOW` clause to explicitly manage and name them distinctly.

WITH
  cte1 AS (
    SELECT
      column1,
      SUM(column1) OVER win_sum AS sum1
    FROM
      table1
  ),
  cte2 AS (
    SELECT
      column2,
      AVG(column2) OVER win_avg AS avg2
    FROM
      table2
  )
SELECT
  * 
FROM cte1 JOIN cte2 ON ...;

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Related Errors

5 related errors

MySQL Error 3591: Duplicate Window Definition