Hi community,
I want to kick off a discussion about deprecating grouped window functions
(GROUP BY TUMBLE/HOP/SESSION) as the table function windowing support
becomes a thing [1] (FROM TABLE(TUMBLE/HOP/SESSION)). The current stage of
table function windowing is TUMBLE support is checked in. HOP and SESSION
support is likely to be merged in 1.23.0.
A briefly example of two different windowing syntax:
// Grouped window functions.
SELECT
product_id, count(*), TUMBLE_START() as window_start
FROM order
GROUP BY product_id, TUMBLE(rowtime, INTERVAL '1' hour); // an hour long
fixed window size.
// Table function windowing syntax.
SELECT
product_id, count(*), window_start
FROM TABLE(TUMBLE(order, DESCRIPTOR(.rowtime), INTERVAL '1' hour)
GROUP BY product_id
I am giving a short, selective comparison as the following:
The places that table function windowing behaves better
1) no GROUPING/GROUP BY enforced. It becomes a problem in streaming JOIN.
For example, one use case is for each hour, apply a JOIN on two streams. In
this case, no GROUP BY is needed.
2) grouped window functions allow multiple calls in GROUP BY. For example,
from SQL syntax perspective, GROUP BY TUMBLE(...), HOP(...), SESSION(...)
is not wrong, but it is an illegal query.
3) Calcite includes an Enumerable implementation of table function
windowing, while grouped window functions do not have that.
The places that table function windowing behaves worse
1) table function windowing adds "window_start", "window_end" into table
directly, which increases the volume of data (number of rows *
sizeof(timestamp) * 2).
I want to focus on discussing two questions in this thread:
1) Do people support deprecating grouped window functions?
2) By which version people prefer to make grouped window functions
completely removed?(if 1) is yes).
[1]: https://jira.apache.org/jira/browse/CALCITE-3271
-Rui
