Preserve NULLs in array_agg pushdown - #340
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Good find. Please add a changelog item and write a descriptive commit 72/50 message in a single commit.
| * length(arr)-n) */ | ||
| CF_ARRAY_SORT_DESC, /* array_sort(arr,desc) → | ||
| * arrayReverseSort/arraySort */ | ||
| CF_ARRAY_AGG, |
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| if ((agg->aggfnoid == F_STRING_AGG_TEXT_TEXT || | ||
| agg->aggfnoid == F_ARRAY_AGG_ANYNONARRAY) && | ||
| agg->aggorder != NIL) { |
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Need test rejecting use of ORDER with F_ARRAY_AGG_ANYNONARRAY
| EXPLAIN (VERBOSE, COSTS OFF) SELECT array_agg(v) FROM agg_bin.null_agg; | ||
| SELECT array_agg(v) FROM agg_bin.null_agg; | ||
| EXPLAIN (VERBOSE, COSTS OFF) SELECT array_agg(v) FROM agg_http.null_agg; | ||
| SELECT array_agg(v) FROM agg_http.null_agg; |
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This is useful but we also need tests to cover all of the variants in deparseArrayAggref(): filter, distinct, and nullable.
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Wrap nullable inputs in tuples before passing them to ClickHouse groupArray so NULL elements are preserved. Keep ordered array_agg local because groupArray does not preserve PostgreSQL ordering. Add regression coverage for nullable, FILTER, DISTINCT, and ORDER BY array_agg variants.
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Summary
ClickHouse groupArray() skips NULL values, while PostgreSQL array_agg() preserves them. Wrap nullable inputs in a tuple before groupArray and unwrap them with arrayMap so NULL elements survive the pushdown.
Non-nullable array_agg() plans keep their existing SQL. Ordered array_agg() stays local because the wrapper does not preserve ordering.
Testing