Github user mmolimar commented on a diff in the pull request:

    https://github.com/apache/spark/pull/18447#discussion_r124545289
  
    --- Diff: 
sql/core/src/test/scala/org/apache/spark/sql/DataFrameFunctionsSuite.scala ---
    @@ -209,6 +209,18 @@ class DataFrameFunctionsSuite extends QueryTest with 
SharedSQLContext {
           Row(2743272264L, 2180413220L))
       }
     
    +  test("misc data_type function") {
    +    val df = Seq(("a", false)).toDF("a", "b")
    +
    +    checkAnswer(
    +      df.select(data_type($"a"), data_type($"b")),
    --- End diff --
    
    The idea would be to know the type based on the value itself, not by the 
schema (i.e. the value could be null):
    ```scala
    val df = spark.sparkContext.parallelize(
          StringData(null) ::
          StringData("a") :: Nil).toDF()
    df.select(data_type(col("s"))) //you get null and string in this case
    df.schema.map(_.dataType.simpleString) // you just get string
    ```
    On the other hand, it'd be nice to have this SQL function as we do in some 
databases.



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