HiveQL Select-Group By

Hive Select-Group By

本章说明SELECT语句中GROUP BY子句的详细信息。GROUP BY子句用于使用特定的收集列将结果集中的所有记录分组。它用于查询一组记录。

句法

GROUP BY子句的语法如下：


SELECT [ALL | DISTINCT] select_expr, select_expr, ... 
FROM table_reference 
[WHERE where_condition] 
[GROUP BY col_list] 
[HAVING having_condition] 
[ORDER BY col_list]] 
[LIMIT number];

例 - 让我们以SELECT…GROUP BY子句为例。假设如下所示的员工表，其中包含ID，姓名，薪水，指定和部门字段。生成查询以检索每个部门的员工人数。


+------+--------------+-------------+-------------------+--------+ 
| ID   | Name         | Salary      | Designation       | Dept   |
+------+--------------+-------------+-------------------+--------+ 
|1201  | Gopal        | 45000       | Technical manager | TP     | 
|1202  | Manisha      | 45000       | Proofreader       | PR     | 
|1203  | Masthanvali  | 40000       | Technical writer  | TP     | 
|1204  | Krian        | 45000       | Proofreader       | PR     | 
|1205  | Kranthi      | 30000       | Op Admin          | Admin  |
+------+--------------+-------------+-------------------+--------+

以下查询使用上述场景检索员工详细信息：


hive> SELECT Dept,count(*) FROM employee GROUP BY DEPT;

成功执行查询后，您将看到以下响应：


+------+--------------+ 
| Dept | Count(*)     | 
+------+--------------+ 
|Admin |    1         | 
|PR    |    2         | 
|TP    |    3         | 
+------+--------------+

使用JDBC程序

下面给出的是JDBC程序，用于给定示例应用Group By子句。


import java.sql.SQLException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.DriverManager;

public class HiveQLGroupBy {
   private static String driverName = "org.apache.hive.jdbc.HiveDriver";
   
   public static void main(String[] args) throws SQLException {
      try {
          // Register driver and create driver instance
         Class.forName(driverName);
         
         // get connection
         Connection con = DriverManager.
         getConnection("jdbc:hive2://localhost:10000/userdb", "", "");
         
         // create statement
         Statement stmt = con.createStatement();
         
         // execute statement
         Resultset res = stmt.execute(“SELECT Dept,count(*) ” + “FROM employee GROUP BY DEPT ”);
         System.out.println(" Dept \t count(*)");
         
         while (res.next()) {
            System.out.println(res.getString(1) + " " + res.getInt(2)); 
         }
         con.close();
      } catch (Exception e) {
         System.out.println(e.getMessage());
      }     
   }
}

将程序保存在名为HiveQLGroupBy.java的文件中。使用以下命令来编译和执行该程序。


$ javac HiveQLGroupBy.java
$ java HiveQLGroupBy

输出：


 Dept     Count(*)
 Admin       1
 PR          2
 TP          3

HiveQL Select-Group By

Hive Select-Group By

句法