Github user petermaxlee commented on a diff in the pull request:
https://github.com/apache/spark/pull/14364#discussion_r72565468
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/FunctionRegistry.scala
---
@@ -452,14 +466,37 @@ object FunctionRegistry {
}
}
- val clazz = tag.runtimeClass
+ (name, (expressionInfo[T](name), builder))
+ }
+
+ /**
+ * Creates a function registry lookup entry for cast aliases
(SPARK-16730).
+ * For example, if name is "int", and dataType is IntegerType, this
means int(x) would become
+ * an alias for cast(x as IntegerType).
+ * See usage above.
+ */
+ private def castAlias(
+ name: String,
+ dataType: DataType): (String, (ExpressionInfo, FunctionBuilder)) = {
+ val builder = (args: Seq[Expression]) => {
+ if (args.size != 1) {
+ throw new AnalysisException(s"Function $name accepts only one
argument")
+ }
+ Cast(args.head, dataType)
+ }
+ (name, (expressionInfo[Cast](name), builder))
--- End diff --
Yes - this is a limitation. That's not what Hive does because Hive actually
does not have a single cast expression. It has a cast expression for each
target type. I think it's a pretty small detail and fixing it would require a
lot of work.
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