Question

我正在尝试使用Spark更改Hive表，例如基于Spark DataFrame输出从Hive表中添加列或删除列。下面是我尝试过的，有点像一个巨大的代码，

    def main(args: Array[String]): Unit = {
    implicit val spark = SparkSession.builder
      .appName("SchemaHandle")
      .enableHiveSupport
      .getOrCreate

    //Assume below is my generated DataFrame
    import spark.implicits._
    val dfSample = Seq(
      (12, "Dallas", "Texas", 55, "BOOK S","hello","Hellotwo"),
      (12, "SF", "CA", 25, "RULER","hello","Hellotwo"),
      (13, "NYC", "NY", 53, "PENCIL S","hello","Hellotwo"),
      (14, "Miami", "Fl", 45, "RULER","hello","Hellotwo"),
      (12, "Houston", "Texas", 75, "MARKER","hello","Hellotwo"),
      (11, "jersey", "NJ", 53, "WHITE NE R","hello","Hellotwo"),
      (19, "new orleans", "LO", 45, "HIGHLIGHTNER","hello","Hellotwo")
    ).toDF("id", "city", "state", "qty", "item","columnone","columntwo")

    try {
      spark.sql("truncate table database.schematest")
      println("Successfully truncated database.schematest")
    } catch {
      case _: Throwable => println("This Job is running for the very first time, so no table to truncate - We'll create the table below")
        dfSample.write.format("parquet").mode(SaveMode.Overwrite).saveAsTable(s"database.schematest")
        println("Output Table Saved to database.schematest")
    }

    //Assume this is Spark DF Schema.
    val seqone: Seq[StructField] = dfSample.schema
    //Assume this is Existing Table Schema.
    val seqtwo: Seq[StructField] = spark.table("database.schematest").schema

    //Get Cols- with Schema to be Added
    val diffedSeq = seqone diff seqtwo
    //Get Cols- with Schema to be Dropped
    val diffedSeqTwo = seqtwo diff seqone

    //Get Cols- names to just make the diff
    val seqonecolumns = dfSample.columns

    //Get Cols- names to just make the diff
    val seqtwocolumns = spark.table("dscoewrk_ing_qa.schematest").columns

    val diffedSeqArrayOne = seqonecolumns diff seqtwocolumns

    val diffedSeqArrayTwo = seqtwocolumns diff seqonecolumns

    var fixedAlterColumns: String = ""
    for (i <- diffedSeqArrayOne) {
      for (j <- diffedSeq) {
        if (i.equals(j.name)) {
          fixedAlterColumns +=""+j.name +" "+ datatypeCheckFunction(j.dataType.toString)+","
        }
      }
    }
    if(fixedAlterColumns.length>0) {
      println(s"Result---> ${fixedAlterColumns.substring(0, fixedAlterColumns.length - 1)}")
      //Lets add new columns to table database.schematest.
      spark.sql(s"ALTER TABLE database.schematest ADD COLUMNS (${fixedAlterColumns.substring(0, fixedAlterColumns.length - 1)})")
      println("Alter Table Success")
    }else{
      println("No Columns to Add")
    }

    println("------------------------------BREAK---------------------------")

    //Now lets think about dropping the columns
    val dfSampleCurrentTable:Seq[StructField] = spark.table("dscoewrk_ing_qa.schematest").schema
    //Since we cannot drop columns from Hive Table, lets do REPLACE COLUMNS.
    val dfSampleFinalDiff = dfSampleCurrentTable diff diffedSeqTwo
    dfSampleFinalDiff.foreach(println)
    val dfSampleFinalDiffColArray = (spark.table("database.schematest").columns) diff diffedSeqArrayTwo
    dfSampleFinalDiffColArray.foreach(println)
    var fixedDropColumns:String = ""

    for(i <- dfSampleFinalDiffColArray){
      println("The i is"+i)
      for(j <-dfSampleCurrentTable){
        println("This is j"+j)
        if(i.equals(j.name)){
          fixedDropColumns+=""+j.name +" "+ datatypeCheckFunction(j.dataType.toString)+","
        }
      }
    }
    //Let's drop the columns that aren't required.

    if(fixedDropColumns.length>0) {
      println(s"Result---> ${fixedDropColumns.substring(0, fixedDropColumns.length - 1)}")
      spark.sql(s"ALTER TABLE database.schematest REPLACE COLUMNS(${fixedDropColumns.substring(0,fixedDropColumns.length-1)})")
      println("Alter Drop Table Success")
    }else{
      println("No Columns to Drop")
    }

    //Now let's save the DF to Output in the Table. By using Append as below.
    dfSample.withColumn("mybool",functions.lit(null)).coalesce(50).write.format("parquet").mode(SaveMode.Append).insertInto("database.schematest")

    println("Saving output Table Successful.")

  }

   def datatypeCheckFunction(datatypePassed: String): String = {
    datatypePassed match {
      case "BinaryType" | "ByteType" | "DateType" | "NullType" | "StringType" | "TimestampType" => "String"
      case "BooleanType" => "boolean"
      case "DoubleType" | "FloatType" => "Double"
      case "IntegerType" | "ShortType" => "Int"
      case "LongType" => "BigInt"
      case _ => "String"
    }
  }
}

我可以理解，还有优化的空间，但是对于此代码，我至少看到了两个问题： 1.当我运行上述Spark作业时，“添加”列成功，但“替换”列失败，如下所示：

Exception in thread "main" org.apache.spark.sql.catalyst.parser.ParseException:
Operation not allowed: ALTER TABLE REPLACE COLUMNS(line 1, pos 0)

== SQL ==
ALTER TABLE database.schematest REPLACE COLUMNS(id Int,city String,state String,qty Int,item String,columnone String,columntwo String)

假设“替换列”有效，是否还会删除该删除列的数据？

这是我使用的Hive创建表语句：

create table schematest(`id` int, `city` string, `state` string, `qty` int, `mybool` boolean) stored as parquet

感谢您的帮助，谢谢大家。

Answer 1

我刚刚在Hive manual中看到了这一段：

REPLACE COLUMNS删除所有现有的列并添加新的列集。仅对具有本地SerDe（DynamicSerDe，MetadataTypedColumnsetSerDe，LazySimpleSerDe和ColumnarSerDe）的表可以做到这一点

据我了解，似乎不支持镶木地板。

如何在不删除配置单元表（例如删除/添加列）的情况下基于DataFrame从SparkSQL更改表？

1 个答案: