Aggregate (window) projection keeps the first value for duplicate output names; non-aggregate keeps the last #47

Summary

In an aggregate (window) query, when two SELECT fields have the same output name, the output keeps the first value. In a non-aggregate query, the same SELECT keeps the last value. The two paths give different results for the same projection.

Revision: 0cda7fddf5777b834b534287246ea4c588abca2b (main after #46).

Where

crates/rekuiper-sql/src/eval.rs, eval_aggregate_stateful (line 291). Every non-aggregate branch writes with entry(..).or_insert.., so a later field cannot replace an earlier value of the same name:

The aggregate-call branch (line 401) uses output.insert(..), and so does the ordinary projection path. So in the aggregate path, the result depends on which branch wrote first.

Reproduction

Rule:

SELECT sum(v) AS x, v AS x, count(*) AS n FROM "order/in" GROUP BY COUNTWINDOW(2)

Input: {"v":1}, then {"v":3}.

• Expected (same rule as the non-aggregate path: first position, last value): {"x":1,"n":2}
• Actual (from the code): {"x":4,"n":2}. sum inserts x=4, then the identifier branch does not replace it.

A second case with a wildcard:

SELECT sum(v) AS v, * FROM "order/in" GROUP BY COUNTWINDOW(2)

• Expected: v stays in the first position and has the first record's raw value, because the later * writes it. Other keys follow in input order.
• Actual: v keeps the sum.

Proposed fix

In eval_aggregate_stateful, write each field with insert in SELECT order, as the non-aggregate path does. IndexMap::insert keeps the first position of an existing key and replaces its value, so the output order from #46 does not change.

Please add regressions for:

• duplicate aliases in a window query;
• an aggregate alias followed by *;
• * followed by an aggregate alias of the same name;
• a GROUP BY key that is selected two times.

The comment at line 409 says the or_insert is there on purpose ("Don't overwrite group keys / wildcard copies"). If that behaviour is required, please document it as the rule for both paths. Only the difference between the two paths is the defect.

Impact

A broker that uses this engine gets different output for the same projection with and without a window. It also cannot give one documented rule for duplicate output names. We found this while we wrote order tests against #46.