[docs] add section for currently unsupported sql operations by anandbraman · Pull Request #5861 · feldera/feldera

anandbraman · 2026-03-18T21:57:58Z

Describe Manual Test Plan

Checklist

Unit tests added/updated
Integration tests added/updated
Documentation updated
Changelog updated

Breaking Changes?

Mark if you think the answer is yes for any of these components:

OpenAPI / REST HTTP API / feldera-types / manager (What is a breaking change?)
Feldera SQL (Syntax, Semantics)
feldera-sqllib (incl. dependencies fxp, etc.) (What is a breaking change?)
Python SDK (What is a breaking change?)
fda (CLI arguments)
Adapters (including configuration)
Storage Format / Checkpoints
Others (specify)

Describe Incompatible Changes

mihaibudiu · 2026-03-18T22:10:55Z

docs.feldera.com/docs/sql/unsupported-operations.md

+
+General-purpose `RANK`, `DENSE_RANK`, and `ROW_NUMBER` outside of TopK
+detection are not yet implemented.
+See [#3934](https://github.com/feldera/feldera/issues/3934).


Also, we can support only 1 topK pattern per OVER query.

mihaibudiu · 2026-03-18T22:13:57Z

docs.feldera.com/docs/sql/unsupported-operations.md

+
+### `FIRST_VALUE` and `LAST_VALUE` limited to unbounded range
+
+`FIRST_VALUE()` and `LAST_VALUE()` are only supported for windows with


An unbounded range is really UNBOUNDED PRECEDING and UNBOUNDED FOLLOWING.
I think we support that too, and up to CURRENT ROW.
But not other things.

Would you recommend I change the word choice? I thought unbounded range could mean that unbounded in one direction or both.

UNBOUNDED usually means in both directions

mihaibudiu · 2026-03-18T22:15:54Z

docs.feldera.com/docs/sql/unsupported-operations.md

+supported.
+See [#457](https://github.com/feldera/feldera/issues/457).
+
+## Correlated subqueries


Also, window boundaries must be constant expressions.
There are expressions like RANGE INTERVAL 1 MONTH PRECEDING which look like constants, but they are not really, because the length of a month is not a constant.

I think that SQL also allows expressions for window boundaries, which don't. We can only handle constant expressions. It is covered by what you way - the example with 1 MONTH looks like a constant expression, but in fact is not.

mihaibudiu · 2026-03-18T22:17:20Z

docs.feldera.com/docs/sql/unsupported-operations.md

+
+## Map functions
+
+Several `MAP` functions are not yet implemented:


Some of these are really Spark specific. They should be in a Spark-specific documents. MAP itself is a non-standard SQL feature.

I could put these under a spark heading, but I don't think we should move it for now. It's easier to manage one page and send users to a single place for "limitations", especially as we update our sql functionality often.

mihaibudiu · 2026-03-18T22:17:57Z

docs.feldera.com/docs/sql/unsupported-operations.md

+
+## Timezone support
+
+`DATE`, `TIME`, and `TIMESTAMP` types have no time zone.  There is no


DATE does not have TIMEZONE ever, not even in standard SQL.
timezones are related to times, they do not apply to dates.

good point, silly error

mihaibudiu · 2026-03-18T22:19:34Z

docs.feldera.com/docs/sql/unsupported-operations.md

+  every step, which can produce large deltas and degrade performance
+  significantly.
+
+See the [datetime documentation](datetime.md#now) for more details.


PIVOT is only supported with a fixed set of columns (we don't support dynamic pivot).
We don't have UNPIVOT yet.

mihaibudiu · 2026-03-18T22:21:26Z

docs.feldera.com/docs/sql/unsupported-operations.md

+
+### `NTILE` is not supported
+
+The `NTILE()` window function is not yet implemented.


Also, nth_value

mihaibudiu · 2026-03-18T22:22:13Z

docs.feldera.com/docs/sql/unsupported-operations.md

+  every step, which can produce large deltas and degrade performance
+  significantly.
+
+See the [datetime documentation](datetime.md#now) for more details.


No support for INTERSECT ALL and EXCEPT ALL.

mihaibudiu · 2026-03-18T22:25:15Z

docs.feldera.com/docs/sql/unsupported-operations.md

+  every step, which can produce large deltas and degrade performance
+  significantly.
+
+See the [datetime documentation](datetime.md#now) for more details.


no support for the MULTISET data type

mihaibudiu · 2026-03-18T22:30:29Z

docs.feldera.com/docs/sql/unsupported-operations.md

+  every step, which can produce large deltas and degrade performance
+  significantly.
+
+See the [datetime documentation](datetime.md#now) for more details.


Sometimes the query decorrelator cannot decorrelate some complex nested subqueries; we cannot execute such queries at all.

I'm going to leave this out for now, unless we have an example of query that we can't decorrelate

There are several issues with the word "decorrelate".
I think you should mention it, even without examples.
Unlike other databases, we cannot run a query which we cannot decorrelate.

added a note

mythical-fred

Mihai's inline comments identify several factual inaccuracies that need to be incorporated before this merges. Please address all of them.

mythical-fred

Addressed. All of Mihai's factual corrections are in — TopK one-per-OVER, constant window bounds, PIVOT/UNPIVOT, INTERSECT ALL/EXCEPT ALL, MULTISET, NTH_VALUE, the DATE timezone error, and the decorrelation note. LGTM.

[docs] add section for currently unsupported sql operations

af61557

anandbraman requested a review from mihaibudiu March 18, 2026 21:58

mihaibudiu reviewed Mar 18, 2026

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mythical-fred suggested changes Mar 19, 2026

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anandbraman added 2 commits March 19, 2026 09:57

updates

c4edd5c

query correlation

038356a

anandbraman requested a review from mihaibudiu March 19, 2026 17:34

mythical-fred approved these changes Mar 19, 2026

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mihaibudiu approved these changes Mar 19, 2026

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anandbraman added this pull request to the merge queue Mar 19, 2026

Merged via the queue into main with commit db79141 Mar 19, 2026
1 check passed

anandbraman deleted the anandraman/fde-29-document-current-limitations-of-feldera-sql-functions branch March 19, 2026 20:23


		### `FIRST_VALUE` and `LAST_VALUE` limited to unbounded range

		`FIRST_VALUE()` and `LAST_VALUE()` are only supported for windows with


		## Map functions

		Several `MAP` functions are not yet implemented:


		## Timezone support

		`DATE`, `TIME`, and `TIMESTAMP` types have no time zone. There is no


		### `NTILE` is not supported

		The `NTILE()` window function is not yet implemented.

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anandbraman commented Mar 18, 2026

Describe Manual Test Plan

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