Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/13966#discussion_r68930450
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/stringExpressions.scala
---
@@ -162,6 +163,46 @@ case class ConcatWs(children: Seq[Expression])
}
}
+@ExpressionDescription(
+ usage = "_FUNC_(n, str1, str2, ...) - returns the n-th string",
+ extended = "> SELECT _FUNC_(1, 'scala', 'java') FROM src LIMIT 1;\n" +
"'scala'")
+case class Elt(children: Seq[Expression])
+ extends Expression with ImplicitCastInputTypes with CodegenFallback {
+
+ private lazy val indexExpr = children.head
+ private lazy val stringExprs = children.tail.toArray
+
+ /** This expression is always nullable because it returns null if index
is out of range. */
+ override def nullable: Boolean = true
+
+ override def dataType: DataType = StringType
+
+ override def inputTypes: Seq[DataType] = IntegerType +:
Seq.fill(children.size - 1)(StringType)
+
+ override def checkInputDataTypes(): TypeCheckResult = {
+ if (children.isEmpty) {
--- End diff --
should we make sure the number of children is greater than 1? What's hive's
hehaviour when call `etl(0)`?
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