Github user bomeng commented on a diff in the pull request:
https://github.com/apache/spark/pull/12373#discussion_r59904696
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/nullExpressions.scala
---
@@ -128,6 +128,143 @@ case class IsNaN(child: Expression) extends
UnaryExpression
}
/**
+ * An Expression accepts two parameters and returns null if both
parameters are equal.
+ * If they are not equal, the first parameter value is returned.
+ */
+@ExpressionDescription(
+ usage = "_FUNC_(a,b) - Returns null if a equals to b, or a otherwise.")
+case class NullIf(left: Expression, right: Expression) extends
BinaryExpression {
+ override def nullable: Boolean = true
+ override def dataType: DataType = left.dataType
+
+ override def eval(input: InternalRow): Any = {
+ val valueLeft = left.eval(input)
+ val valueRight = right.eval(input)
+ if (valueLeft.equals(valueRight)) {
+ null
+ } else {
+ valueLeft
+ }
+ }
+
+ override def genCode(ctx: CodegenContext, ev: ExprCode): String = {
+ val leftGen = left.gen(ctx)
+ val rightGen = right.gen(ctx)
+ s"""
+ ${leftGen.code}
+ ${rightGen.code}
+ boolean ${ev.isNull} = false;
+ ${ctx.javaType(dataType)} ${ev.value} =
${ctx.defaultValue(dataType)};
+ if (${ctx.genEqual(dataType, leftGen.value, rightGen.value)}) {
+ ${ev.isNull} = true;
+ } else {
+ ${ev.value} = ${leftGen.value};
+ }
+ """
+ }
+}
+
+/**
+ * An Expression accepts two parameters and returns the second parameter
if the value
+ * in the first parameter is null; if the first parameter is any value
other than null,
+ * it is returned unchanged.
+ */
+@ExpressionDescription(
+ usage = "_FUNC_(a,b) - Returns b if a is null, or a otherwise.")
+case class Nvl(left: Expression, right: Expression) extends
BinaryExpression {
--- End diff --
I will say, yes, kind of. Here is what I found:
[difference](http://stackoverflow.com/questions/950084/oracle-differences-between-nvl-and-coalesce)
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