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 // To create Dataset<Row> using SparkSession
   Dataset<Row> people = spark.read().parquet("...");
   Dataset<Row> department = spark.read().parquet("...");

   people.filter("age".gt(30))
     .join(department, people.col("deptId").equalTo(department("id")))
     .groupBy(department.col("name"), "gender")
     .agg(avg(people.col("salary")), max(people.col("age")));