This page documents SQL operations and functions that are not yet supported, only partially supported, or should be used with caution in Feldera. These limitations are tracked in our GitHub issue tracker and may be resolved in future releases.

The following aggregate functions are not supported: PERCENTILE_DISC, PERCENTILE_CONT, MODE, CORR, COVAR_POP, COVAR_SAMP, REGR_SLOPE, REGR_INTERCEPT, REGR_R2, JSON_AGG, JSON_OBJECT_AGG, VAR_POP, VAR_SAMP, LISTAGG.

NTILE, NTH_VALUE, PERCENT_RANK, CUME_DIST, VAR_POP, VAR_SAMP window functions are not yet implemented.

FIRST_VALUE() and LAST_VALUE() are only supported for frames whose bounds are UNBOUNDED PRECEDING, CURRENT ROW, or UNBOUNDED FOLLOWING (with RANGE or ROWS): FIRST_VALUE requires the frame to start at UNBOUNDED PRECEDING, and LAST_VALUE requires the frame to end at UNBOUNDED FOLLOWING. Numeric bounds are not yet supported. See #3918.

Window functions using ORDER BY on VARCHAR/STRING, DOUBLE/FLOAT or VARBINARY columns are not yet supported. See #457.

The EXCLUDE clause in window frame specifications is not supported. See #457.

Window functions with ORDER BY on multiple columns are not yet supported. See #457.

Window boundaries must be constant expressions. For example, RANGE BETWEEN INTERVAL 1 DAY PRECEDING AND CURRENT ROW is valid. But RANGE BETWEEN INTERVAL 1 MONTH PRECEDING AND CURRENT ROW is not, because a month is a not a constant time interval.

Some forms of correlated subqueries are not yet implemented and will fail with a "Not yet implemented" error. For example, using UNNEST on a column from an outer query inside an ARRAY subquery is not supported:

-- NOT supported: correlated UNNEST inside ARRAY subquery
SELECT s.id, ARRAY(
    SELECT sp.cell
    FROM UNNEST(s.mentions) AS mention_id
    JOIN spreadsheet sp ON sp.id = mention_id
) AS mentioned_cells
FROM spreadsheet s;

In some instances, Feldera cannot decorrelate complex nested subqueries. In these cases, we recommend users refactor the query.

See #2555.

LEFT JOIN UNNEST(...) and OUTER APPLY (...), are not yet supported:

-- NOT supported: LEFT JOIN UNNEST
SELECT s.id, mention_id
FROM spreadsheet s
LEFT JOIN UNNEST(s.mentions) AS m(mention_id) ON TRUE;

Several MAP functions are not yet implemented:

A list of supported MAP operations is available here. See #1907.

The MATCH_RECOGNIZE clause for pattern matching over rows is not yet supported.

PIVOT is supported if the user provides a fixed set of columns. Refer to PIVOT documentation for example usage. Dynamic PIVOT is not yet supported.

The MULTISET data type is not currently supported.

Session windows (grouping events into sessions based on a gap in activity) are not yet supported.

The type TIME WITH TIME ZONE is not supported.

ARRAY_AGG has O(N) space cost and O(M) work per change, where N is the collection size and M is the total number of elements in modified groups. Consider whether your use case truly requires collecting all values into an array. See the aggregate efficiency documentation for details.

The NOW() function returns the current timestamp and is updated at every processing step (every 100ms by default).

• In filters: NOW() in WHERE clauses for temporal filtering (e.g., WHERE ts >= NOW() - INTERVAL 1 DAY) is efficient and recommended.
• In SELECT or JOIN expressions: Using NOW() in projections (e.g., SELECT col + NOW() FROM T) forces a full table scan at every step, which can produce large deltas and degrade performance significantly.

See the datetime documentation for more details.