SQL 语法风格是指我们查询数据的时候使用 SQL 语句来查询.
    这种风格的查询必须要有临时视图或者全局视图来辅助

    2. scala> val df = spark.read.json("/opt/module/spark-local/examples/src/main/resources/people.json")
    3. df: org.apache.spark.sql.DataFrame = [age: bigint, name: string]
    5. scala> df2.createOrReplaceTempView("people")
    7. scala> spark.sql("select * from people").show
    8. +----+-------+
    9. | age|   name|
    10. +----+-------+
    11. |null|Michael|
    12. |  30|   Andy|
    13. |  19| Justin|
    14. +----+-------+

    注意:
    1.临时视图只能在当前 Session 有效, 在新的 Session 中无效.
    2.可以创建全局视图. 访问全局视图需要全路径:如global_temp.xxx

    1. scala> val df = spark.read.json("/opt/module/spark-local/examples/src/main/resources/people.json")
    2. df: org.apache.spark.sql.DataFrame = [age: bigint, name: string]
    4. scala> df.createGlobalTempView("people")
    6. scala> spark.sql("select * from global_temp.people")
    7. res31: org.apache.spark.sql.DataFrame = [age: bigint, name: string]
    9. scala> res31.show
    10. +----+-------+
    11. | age|   name|
    12. +----+-------+
    13. |null|Michael|
    14. |  30|   Andy|
    15. |  19| Justin|
    16. +----+-------+
    19. scala> spark.newSession.sql("select * from global_temp.people")
    20. res33: org.apache.spark.sql.DataFrame = [age: bigint, name: string]
    22. scala> res33.show
    23. +----+-------+
    24. | age|   name|
    25. +----+-------+
    26. |null|Michael|
    27. |  30|   Andy|
    28. |  19| Justin|
    29. +----+-------+