Github user dbtsai commented on a diff in the pull request:
https://github.com/apache/spark/pull/21848#discussion_r204515560
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
---
@@ -390,6 +390,7 @@ object SimplifyConditionals extends Rule[LogicalPlan]
with PredicateHelper {
case If(TrueLiteral, trueValue, _) => trueValue
case If(FalseLiteral, _, falseValue) => falseValue
case If(Literal(null, _), _, falseValue) => falseValue
+ case If(_, trueValue, falseValue) if
trueValue.semanticEquals(falseValue) => trueValue
--- End diff --
Can you elaborate?
For `trueValue.semanticEquals(falseValue)`, it's guaranteed that both
`trueValue` and `falseValue` are `deterministic`.
```scala
def semanticEquals(other: Expression): Boolean =
deterministic && other.deterministic && canonicalized ==
other.canonicalized
```
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