spark union和hive union的区别

spark中data frame 有union和union all算子，均不去重
这点，不像hive中那样，hive sql中union all不去重，union去重

示例

	val df3: DataFrame = sc.makeRDD(Seq((1, "xm"), (2, "xl"))).toDF("id", "name")
    val df4: DataFrame = sc.makeRDD(Seq((1, "xm"), (2, "xl"), (3, "xw"))).toDF("id", "name")

    df3.union(df4).show(false)
   +---+----+
	|id |name|
	+---+----+
	|1  |xm  |
	|2  |xl  |
	|1  |xm  |
	|2  |xl  |
	|3  |xw  |
	+---+----+

    df3.unionAll(df4).show(false)
    +---+----+
	|id |name|
	+---+----+
	|1  |xm  |
	|2  |xl  |
	|1  |xm  |
	|2  |xl  |
	|3  |xw  |
	+---+----+

如果想达到hive中的效果，可以使用distinct算子

 df3.union(df4).distinct().show(false)
 
+---+----+
|id |name|
+---+----+
|1  |xm  |
|3  |xw  |
|2  |xl  |
+---+----+