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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