Gustavo de Morais created FLINK-39202:
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Summary: Simplify COALESCE expressions referencing equi-join
columns
Key: FLINK-39202
URL: https://issues.apache.org/jira/browse/FLINK-39202
Project: Flink
Issue Type: Improvement
Components: Table SQL / API
Affects Versions: 2.2.0
Reporter: Gustavo de Morais
Assignee: Gustavo de Morais
Fix For: 2.3.0
Add a new planner rule SimplifyCoalesceWithEquiJoinConditionRule that replaces
COALESCE(a, b) with a direct column reference when both arguments reference
opposite sides of an equi-join condition.
For example, SELECT COALESCE(b.id, a.id) FROM t1 a LEFT JOIN t2 b ON a.id =
b.id simplifies to a.id, since the left side is always non-null in a LEFT JOIN.
The rule handles LEFT, RIGHT, and INNER joins, skips FULL OUTER, and supports
Project and Calc nodes. Supports both batch and stream rule sets.
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