本章介紹了如何使用SELECT語句的ORDER BY子句。ORDER BY子句用於檢索基於一列的細節並設置排序結果按升序或降序排列。

語法

下麵給出的是ORDER BY子句的語法：

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];

示例

讓我們舉個SELECT ... ORDER BY子句的例子。假設員工表，如下Id, Name, Salary, Designation, 和 Dept 的字段，生成一個查詢用於檢索員工的詳細信息。

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

下麵是使用上述業務情景查詢檢索員工詳細信息：

hive> SELECT Id, Name, Dept FROM employee ORDER BY DEPT;

成功執行查詢後，能看到以下回應：

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

JDBC 程序

下麵是JDBC程序應用給定Order By子句的例子。

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

public class HiveQLOrderBy {
   private static String driverName = "org.apache.hadoop.hive.jdbc.HiveDriver";
   
   public static void main(String[] args) throws SQLException {
   
      // Register driver and create driver instance
      Class.forName(driverName);
      
      // get connection
      Connection con = DriverManager.getConnection("jdbc:hive://localhost:10000/userdb", "", "");
      
      // create statement 
      Statement stmt = con.createStatement();
      
      // execute statement
      Resultset res = stmt.executeQuery("SELECT * FROM employee ORDER BY DEPT;");
      System.out.println(" ID \t Name \t Salary \t Designation \t Dept ");
      
      while (res.next()) {
         System.out.println(res.getInt(1) + " " + res.getString(2) + " " + res.getDouble(3) + " " + res.getString(4) + " " + res.getString(5));
      }
      
      con.close();
   }
}

保存程序在一個名為HiveQLOrderBy.java文件。使用下麵的命令來編譯並執行這個程序。

$ javac HiveQLOrderBy.java
$ java HiveQLOrderBy

輸出

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