Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/10577#discussion_r49915984
--- Diff:
sql/hive/src/main/scala/org/apache/spark/sql/hive/SQLBuilder.scala ---
@@ -129,12 +129,16 @@ class SQLBuilder(logicalPlan: LogicalPlan,
sqlContext: SQLContext) extends Loggi
conditionSQL = condition.sql
} yield s"$childSQL $whereOrHaving $conditionSQL"
- case Union(left, right) =>
+ case Union(children) if children.length > 1 =>
for {
- leftSQL <- toSQL(left)
- rightSQL <- toSQL(right)
+ leftSQL <- toSQL(children.head)
+ // When children.tail only has one child, we will go to the next
case to get rid of Union.
+ rightSQL <- toSQL(Union(children.tail))
} yield s"$leftSQL UNION ALL $rightSQL"
--- End diff --
how about
```
val childrenSql = children.map(toSQL)
if (childrenSql.exists(_.isEmpty)) {
None
} else {
childrenSql.map(_.get).mkString("UNION ALL")
}
```
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