Spark SQL scala DSL子查询支持

 SELECT A.dep_id,
        A.employee_id,
        A.age,
       (SELECT  MAX(age) 
          FROM employee B 
         WHERE A.dep_id = B.dep_id) max_age
 FROM     employee A
 ORDER BY 1,2

sql("SELECT COUNT(*) FROM src").show()
val sqlDF = sql("SELECT key, value FROM src WHERE key < 10 ORDER BY key") 
val stringsDS = sqlDF.map {case Row(key: Int, value: String) => s"Key: $key, Value: $value"}
stringsDS.show()