Github user dongjoon-hyun commented on a diff in the pull request:
https://github.com/apache/spark/pull/14048#discussion_r69662351
--- Diff: sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala ---
@@ -184,7 +183,8 @@ class Dataset[T] private[sql](
// to happen right away to let these side effects take place eagerly.
case p if hasSideEffects(p) =>
LogicalRDD(queryExecution.analyzed.output,
queryExecution.toRdd)(sparkSession)
- case Union(children) if children.forall(hasSideEffects) =>
+ case Union(children) if children.forall(x =>
+ x.isInstanceOf[InsertIntoTable] ||
x.isInstanceOf[InsertIntoHadoopFsRelationCommand]) =>
--- End diff --
Please consider the following example in the current master. This PR blocks
this kind of weird behavior.
```
scala> spark.emptyDataFrame.createOrReplaceTempView("empty")
scala> sql("CREATE TABLE tbl(i INT) USING PARQUET")
scala> sql("(INSERT INTO tbl VALUES(1)) UNION ALL (INSERT INTO tbl
VALUES(2))")
scala> sql("select * from tbl").collect()
res4: Array[org.apache.spark.sql.Row] = Array([1], [2])
scala> sql("(INSERT INTO tbl VALUES(5)) UNION ALL (SELECT * FROM empty)")
scala> sql("select * from tbl").collect()
res6: Array[org.apache.spark.sql.Row] = Array([1], [2])
```
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