[SPARK-51040] Enforce determinism when assigning implicit aliases to collation types #49735
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What changes were proposed in this pull request?
This PR proposes a change that enforces determinism when assigning implicit aliases to collation types.
Why are the changes needed?
With the current implementation,
Aliascan be computed both before and after type coercion rule. This will cause non-deterministic behavior when assigning implicit aliases to objects that are (or will be) type coerced to collation type.Given a query like:
select concat_ws(' ' collate utf8_lcase, utf8_binary, 'SQL' collate utf8_lcase) from t5will produce output schema:
concat_ws(collate( , utf8_lcase), utf8_binary, collate(SQL, utf8_lcase))On the other hand, query like:
select 'a' collate unicode < 'A'will produce output schema:
(collate(a, unicode) < 'A' collate UNICODE)This PR will remove
collatefrom alias, making it deterministic in all cases.Does this PR introduce any user-facing change?
Yes. Output schema will be changed in certain cases, as mentioned above.
How was this patch tested?
Modified existing tests.
Was this patch authored or co-authored using generative AI tooling?
No