Vitalii Li created SPARK-39169:
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Summary: Optimize FIRST when used as non-aggregate
Key: SPARK-39169
URL: https://issues.apache.org/jira/browse/SPARK-39169
Project: Spark
Issue Type: Improvement
Components: SQL
Affects Versions: 3.3.0
Reporter: Vitalii Li
When `FIRST` is a single aggregate function in `Aggregate` we could either
rewrite whole query or optimize execution logic.
* Plan => `SELECT FIRST(<col>) FROM <table> [GROUP BY <col>]` => `SELECT <col>
FROM <table> LIMIT 1`. Note that setting `ignoreNulls` to `true` should block
such rewrite since returns could differ in case all values of <col> are `NULL`
* Execution => `SELECT FIRST(<col>) FROM <table> GROUP BY <col2>` => short
circuit iteration per key once a value for `FIRST` is set.
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