Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/7157#discussion_r33864982
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala
---
@@ -167,6 +167,25 @@ abstract class BinaryExpression extends Expression
with trees.BinaryNode[Express
override def toString: String = s"($left $symbol $right)"
+ // Default behavior of evaluation according to the default nullability
of BinaryExpression.
+ // If subclass of BinaryExpression override nullable, probably should
also override this.
+ override def eval(input: InternalRow): Any = {
+ val evalE1 = left.eval(input)
+ if(evalE1 == null) {
+ null
+ } else {
+ val evalE2 = right.eval(input)
+ if (evalE2 == null) {
+ null
+ } else {
+ nullSafeEval(evalE1, evalE2)
+ }
+ }
+ }
+
+ protected def nullSafeEval(evalE1: Any, evalE2: Any): Any =
+ sys.error(s"BinaryExpressions must override either eval or
nullSafeEval")
--- End diff --
There maybe exceptional cases that user need to override `eval`, at that
time they don't need to implement `nullSafeEval`.
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