SQL WINDOW

What does the SQL WINDOW clause do?

Defines one or more named window specifications that analytic functions can reference with OVER().

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Compatible dialects for SQL WINDOW: PostgreSQL 8.4+, MySQL 8.0+, MariaDB 10.2+, SQLite (not yet), SQL Server (not supported), Oracle (not supported as of 23c), DuckDB, Trino/Presto, BigQuery

SQL WINDOW Full Explanation

The WINDOW clause is part of the SELECT statement in the SQL standard. Positioned after GROUP BY and HAVING (if present) and before ORDER BY, it lets you declare reusable, named window definitions. Each name captures the partitioning, ordering, and frame boundaries that window (analytic) functions require. By centralizing the definition, you avoid repeating identical OVER() clauses, keep queries readable, and guarantee that multiple aggregates operate over the exact same rows.A window specification can inherit another named window and extend or override parts of it. This composability supports complex analytics while minimizing duplication.Caveats:- WINDOW is not available in every database even if that database supports window functions.- Names must be unique within the statement.- A named window cannot reference itself, and cyclical inheritance is prohibited.- A named window cannot include another WINDOW clause.Behavior is purely logical: WINDOW only defines scopes; it does not change the result set until paired with analytic functions.

SQL WINDOW Syntax

SELECT column_list
FROM   table_name
[WHERE  conditions]
[GROUP BY grouping_columns]
[HAVING having_condition]
WINDOW window_name AS (window_definition)
       [, window_name2 AS (window_definition2) ...]
[ORDER BY order_columns];

SQL WINDOW Parameters

window_name (identifier) - Label used later inside OVER(window_name)
window_definition (clause) - PARTITION BY, ORDER BY, and frame specification that describe the window

Example Queries Using SQL WINDOW

-- 1. Simple reuse across two aggregates
SELECT id,
       SUM(amount)   OVER monthly_sales     AS total_amount,
       AVG(amount)   OVER monthly_sales     AS avg_amount
FROM   orders
WINDOW monthly_sales AS (
  PARTITION BY DATE_TRUNC('month', order_date)
  ORDER BY order_date
);

-- 2. Inheriting and extending a window
SELECT id,
       SUM(amount) OVER monthly_sales           AS total_amount,
       SUM(amount) OVER monthly_sales_rows10    AS rolling_10
FROM   orders
WINDOW monthly_sales AS (
         PARTITION BY DATE_TRUNC('month', order_date)
         ORDER BY order_date
       ),
       monthly_sales_rows10 AS (
         monthly_sales ROWS BETWEEN 9 PRECEDING AND CURRENT ROW
       );

Expected Output Using SQL WINDOW

Each analytic function returns its calculation over the named window
The first query outputs two columns per row: total_amount and avg_amount, both calculated per month without writing the window definition twice

Use Cases with SQL WINDOW

Writing multiple analytic functions that share identical PARTITION BY/ORDER BY
Building layered analytics where one window inherits another but adds a frame
Making long, complex SELECTs easier to maintain and review
Guaranteeing consistency across metrics in BI dashboards or reports

Common Mistakes with SQL WINDOW

Assuming WINDOW is supported in every database with window functions
Forgetting to place the WINDOW clause before ORDER BY, causing syntax errors
Using duplicate window names in the same statement
Adding SELECT columns inside the window_definition (only PARTITION BY, ORDER BY, frame are allowed)

First Introduced In

SQL:2003

Frequently Asked Questions

What databases support the WINDOW clause?

PostgreSQL, MySQL 8.0, MariaDB, DuckDB, Trino, BigQuery, and most engines that closely follow the SQL standard. SQL Server and Oracle currently lack support.

How is WINDOW different from OVER()?

OVER() attaches a window to an individual analytic function. WINDOW defines the window once and lets many OVER(window_name) references reuse it, keeping the query concise.

Can I use multiple WINDOW clauses in one SELECT?

Yes. You can list multiple name-definition pairs separated by commas within a single WINDOW clause block.

Does WINDOW affect performance?

Performance is usually unchanged. It only removes duplication in the query text. The optimizer still evaluates each analytic function, often sharing computation when possible.