Github user gczsjdy commented on a diff in the pull request: https://github.com/apache/spark/pull/20135#discussion_r159234455 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/stringExpressions.scala --- @@ -271,33 +271,45 @@ case class ConcatWs(children: Seq[Expression]) } } +/** + * An expression that returns the `n`-th input in given inputs. + * If all inputs are binary, `elt` returns an output as binary. Otherwise, it returns as string. + * If any input is null, `elt` returns null. + */ // scalastyle:off line.size.limit @ExpressionDescription( - usage = "_FUNC_(n, str1, str2, ...) - Returns the `n`-th string, e.g., returns `str2` when `n` is 2.", + usage = "_FUNC_(n, input1, input2, ...) - Returns the `n`-th input, e.g., returns `input2` when `n` is 2.", examples = """ Examples: > SELECT _FUNC_(1, 'scala', 'java'); scala """) // scalastyle:on line.size.limit -case class Elt(children: Seq[Expression]) - extends Expression with ImplicitCastInputTypes { +case class Elt(children: Seq[Expression]) extends Expression { private lazy val indexExpr = children.head - private lazy val stringExprs = children.tail.toArray + private lazy val inputExprs = 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 dataType: DataType = inputExprs.map(_.dataType).headOption.getOrElse(StringType) --- End diff -- Should we return null of `BinaryType` when `eltOutputAsString` is `false` and there's only 1 parameter for `Elt`?
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