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Improve named window documentation re. name scopes.

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Adriano dos Santos Fernandes 2018-12-16 18:27:00 -02:00
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doc/sql.extensions/README.window_functions.md
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@ -354,6 +354,8 @@ Some window functions discard frames. `ROW_NUMBER`, `LAG` and `LEAD` always work
To avoid write repetitive or confusing expressions, windows can be named in a query with the `WINDOW` clause. A named window can be used in `OVER` to reference a window definition and can also be used as a base window of another named or inline (`OVER`) window. A window with frame (`ROWS` or `RANGE` clauses) can't be used as base window (but can be used with `OVER <window name>`). And a window with a base window can't have `PARTITION BY` nor can override `ORDER BY` of a base window. To avoid write repetitive or confusing expressions, windows can be named in a query with the `WINDOW` clause. A named window can be used in `OVER` to reference a window definition and can also be used as a base window of another named or inline (`OVER`) window. A window with frame (`ROWS` or `RANGE` clauses) can't be used as base window (but can be used with `OVER <window name>`). And a window with a base window can't have `PARTITION BY` nor can override `ORDER BY` of a base window.
In a query with multiple `SELECT` and `WINDOW` clauses (for example, with subqueries), the window name scope is bound only to its query context, that is, a window name from an inner or outer context could not be used in another context. As such, the same window name definition could be used at different contexts.
Example query with named windows: Example query with named windows:
```sql ```sql