mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-16 03:12:43 +00:00
58 lines
2.5 KiB
Markdown
58 lines
2.5 KiB
Markdown
---
|
|
sidebar_position: 62
|
|
sidebar_label: Window Functions
|
|
---
|
|
|
|
# Window Functions
|
|
|
|
ClickHouse supports the standard grammar for defining windows and window functions. The following features are currently supported:
|
|
|
|
| Feature | Support or workaround |
|
|
| --------| ----------|
|
|
| ad hoc window specification (`count(*) over (partition by id order by time desc)`) | supported |
|
|
| expressions involving window functions, e.g. `(count(*) over ()) / 2)` | not supported, wrap in a subquery ([feature request](https://github.com/ClickHouse/ClickHouse/issues/19857)) |
|
|
| `WINDOW` clause (`select ... from table window w as (partition by id)`) | supported |
|
|
| `ROWS` frame | supported |
|
|
| `RANGE` frame | supported, the default |
|
|
| `INTERVAL` syntax for `DateTime` `RANGE OFFSET` frame | not supported, specify the number of seconds instead |
|
|
| `GROUPS` frame | not supported |
|
|
| Calculating aggregate functions over a frame (`sum(value) over (order by time)`) | all aggregate functions are supported |
|
|
| `rank()`, `dense_rank()`, `row_number()` | supported |
|
|
| `lag/lead(value, offset)` | Not supported. Workarounds: |
|
|
| | 1) replace with `any(value) over (.... rows between <offset> preceding and <offset> preceding)`, or `following` for `lead`|
|
|
| | 2) use `lagInFrame/leadInFrame`, which are analogous, but respect the window frame. To get behavior identical to `lag/lead`, use `rows between unbounded preceding and unbounded following` |
|
|
|
|
## References
|
|
|
|
### GitHub Issues
|
|
|
|
The roadmap for the initial support of window functions is [in this issue](https://github.com/ClickHouse/ClickHouse/issues/18097).
|
|
|
|
All GitHub issues related to window funtions have the [comp-window-functions](https://github.com/ClickHouse/ClickHouse/labels/comp-window-functions) tag.
|
|
|
|
### Tests
|
|
|
|
These tests contain the examples of the currently supported grammar:
|
|
|
|
https://github.com/ClickHouse/ClickHouse/blob/master/tests/performance/window_functions.xml
|
|
|
|
https://github.com/ClickHouse/ClickHouse/blob/master/tests/queries/0_stateless/01591_window_functions.sql
|
|
|
|
### Postgres Docs
|
|
|
|
https://www.postgresql.org/docs/current/sql-select.html#SQL-WINDOW
|
|
|
|
https://www.postgresql.org/docs/devel/sql-expressions.html#SYNTAX-WINDOW-FUNCTIONS
|
|
|
|
https://www.postgresql.org/docs/devel/functions-window.html
|
|
|
|
https://www.postgresql.org/docs/devel/tutorial-window.html
|
|
|
|
### MySQL Docs
|
|
|
|
https://dev.mysql.com/doc/refman/8.0/en/window-function-descriptions.html
|
|
|
|
https://dev.mysql.com/doc/refman/8.0/en/window-functions-usage.html
|
|
|
|
https://dev.mysql.com/doc/refman/8.0/en/window-functions-frames.html
|