Github user myui commented on a diff in the pull request:
https://github.com/apache/incubator-hivemall/pull/61#discussion_r105071319
--- Diff:
spark/spark-2.1/src/main/scala/org/apache/spark/sql/hive/HivemallOps.scala ---
@@ -805,6 +805,47 @@ final class HivemallOps(df: DataFrame) extends Logging
{
JoinTopK(kInt, df.logicalPlan, right.logicalPlan, Inner,
Option(joinExprs.expr))(score.named)
}
+ private def doFlatten(schema: StructType, prefix: Option[String] = None)
: Seq[Column] = {
+ schema.fields.flatMap { f =>
+ val colName = prefix.map(p => s"$p.${f.name}").getOrElse(f.name)
--- End diff --
Dot `.` is a special symbol in SQL. So, better to change the default
separator (e.g., `$` ) and have an option to choose the separator.
`news20.train` means train table in news20 database.
SQL identifiers are depending on RDBMSs but generally includes
`[0-9,a-z,A-Z$_]`.
https://www.postgresql.org/docs/9.1/static/sql-syntax-lexical.html
https://msdn.microsoft.com/en-us/library/ms175874.aspx
https://dev.mysql.com/doc/refman/5.7/en/identifiers.html
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