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Data Types

DataType is the base type of all the data types in Spark SQL.

Built-in data types belong to the org.apache.spark.sql.types package.

A schema is the description of the structure of your data (which together create a Dataset in Spark SQL). It can be implicit (and inferred at runtime) or explicit (and known at compile time).

val df = Seq((0, s"""hello\tworld"""), (1, "two  spaces inside")).toDF("label", "sentence")

scala> df.printSchema
 |-- label: integer (nullable = false)
 |-- sentence: string (nullable = true)

scala> df.schema
res0: org.apache.spark.sql.types.StructType = StructType(StructField(label,IntegerType,false), StructField(sentence,StringType,true))

scala> df.schema("label").dataType
res1: org.apache.spark.sql.types.DataType = IntegerType

A schema is described using StructType which is a collection of StructFields (that in turn are tuples of names, types, and nullability classifier).

import org.apache.spark.sql.types.{IntegerType, StringType}
val schemaTyped = new StructType()
  .add("a", IntegerType)
  .add("b", StringType)

DataTypes utility can be used to create data types.

import org.apache.spark.sql.types.DataTypes._
val schemaWithMap = StructType(
  StructField("map", createMapType(LongType, StringType), false) :: Nil)

CatalystSqlParser is responsible for parsing data types.

Encoder allows describing the schema in a type-safe manner.

import org.apache.spark.sql.Encoders

scala> Encoders.INT.schema.printTreeString
 |-- value: integer (nullable = true)

scala> Encoders.product[(String, java.sql.Timestamp)].schema.printTreeString
|-- _1: string (nullable = true)
|-- _2: timestamp (nullable = true)

case class Person(id: Long, name: String)
scala> Encoders.product[Person].schema.printTreeString
 |-- id: long (nullable = false)
 |-- name: string (nullable = true)

StructType gives printTreeString that makes presenting the schema more user-friendly.

scala> schemaTyped.printTreeString
 |-- a: integer (nullable = true)
 |-- b: string (nullable = true)

scala> schemaWithMap.printTreeString
|-- map: map (nullable = false)
|    |-- key: long
|    |-- value: string (valueContainsNull = true)

// You can use prettyJson method on any DataType
scala> println(schema1.prettyJson)
 "type" : "struct",
 "fields" : [ {
   "name" : "a",
   "type" : "integer",
   "nullable" : true,
   "metadata" : { }
 }, {
   "name" : "b",
   "type" : "string",
   "nullable" : true,
   "metadata" : { }
 } ]
import org.apache.spark.sql.types.StructType
val schemaUntyped = new StructType()
  .add("a", "int")
  .add("b", "string")
// alternatively using Schema DSL
val schemaUntyped_2 = new StructType()