2.5 KiB
| toc_priority | toc_title |
|---|---|
| 62 | Window Functions |
[experimental] 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) |
WINDOW clause (select ... from table window w as (partiton 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.
All GitHub issues related to window funtions have the 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
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