Spark withColumn 和 where 执行顺序答案

【问题标题】：Spark withColumn and where execution orderSpark withColumn 和 where 执行顺序
【发布时间】：2020-01-16 11:42:21
【问题描述】：

我有一个 Spark 查询，它从 S3 读取大量镶木地板数据，对其进行过滤，并添加一个计算为 regexp_extract(input_file_name, ...) 的列，我认为这是一个相对繁重的操作（如果在过滤之前而不是之后应用）。

整个查询如下所示：

val df = spark
    .read
    .option("mergeSchema", "true")
    .parquet("s3://bucket/path/date=2020-01-1{5,6}/clientType=EXTENSION_CHROME/type={ACCEPT,IGNORE*}/")
    .where(...)
    .withColumn("type", regexp_extract(input_file_name, "type=([^/]+)", 1))
    .repartition(300)
    .cache()

df.count()

withColumn 是在 where 之后还是在 where 之前执行的？这取决于我写它们的顺序吗？如果我的 where 语句使用了 withColumn 添加的列怎么办？

【问题讨论】：

标签： scala apache-spark apache-spark-sql

【解决方案1】：

withColumn 和 filter 按照调用顺序执行。该计划对此进行了解释。请自下而上阅读计划。

val employees = spark.createDataFrame(Seq(("E1",100.0), ("E2",200.0),("E3",300.0))).toDF("employee","salary")

employees.withColumn("column1", when(col("salary") > 200, lit("rich")).otherwise("poor")).filter(col("column1")==="poor").explain(true)

计划 - 项目首先发生，然后过滤。

== Parsed Logical Plan ==
'Filter ('column1 = poor)
+- Project [employee#4, salary#5, CASE WHEN (salary#5 > cast(200 as double)) THEN rich ELSE poor END AS column1#8]
   +- Project [_1#0 AS employee#4, _2#1 AS salary#5]
      +- LocalRelation [_1#0, _2#1]

== Analyzed Logical Plan ==
employee: string, salary: double, column1: string
Filter (column1#8 = poor)
+- Project [employee#4, salary#5, CASE WHEN (salary#5 > cast(200 as double)) THEN rich ELSE poor END AS column1#8]
   +- Project [_1#0 AS employee#4, _2#1 AS salary#5]
      +- LocalRelation [_1#0, _2#1]

代码 1st 过滤器然后添加新列

employees.filter(col("employee")==="E1").withColumn("column1", when(col("salary") > 200, lit("rich")).otherwise("poor")).explain(true)

计划 - 第一个过滤器然后是项目

== Parsed Logical Plan ==
'Project [employee#4, salary#5, CASE WHEN ('salary > 200) THEN rich ELSE poor END AS column1#13]
+- Filter (employee#4 = E1)
   +- Project [_1#0 AS employee#4, _2#1 AS salary#5]
      +- LocalRelation [_1#0, _2#1]

== Analyzed Logical Plan ==
employee: string, salary: double, column1: string
Project [employee#4, salary#5, CASE WHEN (salary#5 > cast(200 as double)) THEN rich ELSE poor END AS column1#13]
+- Filter (employee#4 = E1)
   +- Project [_1#0 AS employee#4, _2#1 AS salary#5]
      +- LocalRelation [_1#0, _2#1]

另一个证据 - 在添加之前在列上调用过滤器时会出错（显然）

employees.filter(col("column1")==="poor").withColumn("column1", when(col("salary") > 200, lit("rich")).otherwise("poor")).show()

org.apache.spark.sql.AnalysisException: cannot resolve '`column1`' given input columns: [employee, salary];;
'Filter ('column1 = poor)
+- Project [_1#0 AS employee#4, _2#1 AS salary#5]
   +- LocalRelation [_1#0, _2#1]

【讨论】：