Github user tejasapatil commented on a diff in the pull request:
https://github.com/apache/spark/pull/17993#discussion_r118849967
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
---
@@ -54,6 +54,62 @@ object ConstantFolding extends Rule[LogicalPlan] {
}
}
+/**
+ * Substitutes [[Attribute Attributes]] which can be statically evaluated
with their corresponding
+ * value in conjunctive [[Expression Expressions]]
+ * eg.
+ * {{{
+ * SELECT * FROM table WHERE i = 5 AND j = i + 3
+ * ==> SELECT * FROM table WHERE i = 5 AND j = 8
+ * }}}
+ *
+ * Approach used:
+ * - Start from AND operator as the root
+ * - Get all the children conjunctive predicates which are EqualTo /
EqualNullSafe such that they
+ * don't have a `NOT` or `OR` operator in them
+ * - Populate a mapping of attribute => constant value by looking at all
the equals predicates
+ * - Using this mapping, replace occurrence of the attributes with the
corresponding constant values
+ * in the AND node.
+ */
+object ConstantPropagation extends Rule[LogicalPlan] with PredicateHelper {
+ def containsNonConjunctionPredicates(expression: Expression): Boolean =
expression.find {
+ case _: Not | _: Or => true
+ case _ => false
+ }.isDefined
+
+ def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+ case f: Filter => f transformExpressionsUp {
--- End diff --
Yes the result should be the same. I don't have any theoretical proof if
doing this over joins will be safe so want to be cautious here ... any bad
rules might lead to correctness bugs which is super bad for end users.
> it would be nice if these constraints are at least generated here
Sorry I am not able to get you here and want to make sure if I am not
ignoring your comment. Are you suggesting any changes over the existing version
?
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