SparkSQL - NULL值多组测试结果

有很多种情况，spark sql语句中的某些字段是空的，想要知道sql中聚合函数对null的影响结果，下面做了几个测试用例。

image.png

测试用例

准备三个case class

case class ChildLog(id:String,name:String)
case class WifeLog(id:String,name:String,child:ChildLog)
case class UserLog(id:String,name:String,wife:WifeLog)

准备三组数据

val list1 = Array(UserLog("1", "lake", null), UserLog("2", "admin", null))
val list2 = Array(UserLog("1", "lake", WifeLog(null,null,null)), UserLog("2", "admin", WifeLog("3", "coco",null)))
val list3 = Array(UserLog("1", "lake", WifeLog(null,null,ChildLog("hi","na"))), UserLog("2", "admin", WifeLog("3", "coco",null)))

初始化环境

val sparkConf = new SparkConf()
      .setMaster("local[1]")
      .setAppName("testNull")

    val spark = SparkSession
      .builder
      .config(sparkConf)
      .getOrCreate()

    val sc = spark.sparkContext

第一组

1. 测试count对null值的结果

val list1 = Array(UserLog("1", "lake", null), UserLog("2", "admin", WifeLog("3", "coco",null)))
val listRdd = sc.parallelize(list3)

listRdd.toDS().createTempView("log")

spark.sql("select count(wife) from log").show

结果(对空值会忽略)

+-----------+
|count(wife)|
+-----------+
|          1|
+-----------+

结论(如下两个语句相等)

spark.sql("select count(wife) from log").show
spark.sql("select count(wife) from log where wife IS NOT NULL").show

2. 如何统计null

spark.sql("select count(wife IS NULL) from log where").show

结果

+---------------------+
|count((wife IS NULL))|
+---------------------+
|                    1|
+---------------------+

第二组

1. 测试子类case

spark.sql("select count(wife.id) from log").show

结果

+----------------------+
|count(wife.id AS `id`)|
+----------------------+
|                     1|
+----------------------+

结论(对子类case的空值也会忽略,对空的子类也会忽略)

第三组

测试多级子case的影响

spark.sql("select count(wife.child.id) from log").show

结果

+----------------------------+
|count(wife.child.id AS `id`)|
+----------------------------+
|                           1|
+----------------------------+

结论(不论子级多深,只统计非空值的数据)

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