viirya commented on code in PR #36455:
URL: https://github.com/apache/spark/pull/36455#discussion_r866406148
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala:
##########
@@ -454,6 +454,33 @@ trait Nondeterministic extends Expression {
protected def evalInternal(input: InternalRow): Any
}
+/**
+ * An expression that contains predicate expression branch, so not all branch
will be hit
+ * at runtime. All optimization should be careful with the evaluation order.
+ */
+trait ConditionalExpression extends Expression {
+ /**
+ * Return the expression which can always be hit at runtime, For example:
+ * 1. If: common subexpressions will always be evaluated at the beginning,
but the true and
+ * false expressions in `If` may not get accessed, according to the
predicate
+ * expression. We should only return the predicate expression.
+ * 2. CaseWhen: like `If`, the children of `CaseWhen` only get accessed in a
certain
+ * condition. We should only return the first condition
expression as it
+ * will always get accessed.
+ * 3. Coalesce: it's also a conditional expression, we should only return
the first child,
+ * because others may not get accessed.
+ * 4. NaNvl: we can only guarantee the left child can be always accessed.
+ * And if we hit the left child, the right will not be accessed.
+ */
+ def head: Expression = children.head
Review Comment:
+1 for `Seq[Expression]` for 1.
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: [email protected]
For queries about this service, please contact Infrastructure at:
[email protected]
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
