ORDER BY子句用于按照使用关键字的顺序排列结果集的内容,ASC表示升序,DESC表示降序.如果你没有提到其中任何一个,默认情况下内容将按升序排列.
以下是ORDER的语法BY子句 :
SELECT * FROM table_name ORDER BY column_name ASC|DESC.
假设我们在数据库中有一个名为Employees的表,其中包含以下记录 :
ID |NAME |SALARY |LOCATION ------------------------------------------------------------------------------ 1 |Amit |30000 |Vijayawada 2 |Kalyan |40000 |Vishakhapatnam 3 |Renuka |50000 |Delhi 4 |Archana |15000 |Vijayawada 5 |Trupthi |45000 |Kochin 6 |Suchatra |33000 |Vijayawada 7 |Rahul |39000 |Lucknow
以下查询根据Employee的名称按升序排列表的内容.
ij> SELECT * FROM Employees ORDER BY Name;
这将产生以下输出 :
ID |NAME |SALARY |LOCATION --------------------------------------------------------------- 1 |Amit |30000 |Hyderabad 4 |Archana |15000 |Mumbai 2 |Kalyan |40000 |Vishakhapatnam 7 |Rahul |39000 |Lucknow 3 |Renuka |50000 |Delhi 6 |Suchatra |33000 |Pune 5 |Trupthi |45000 |Kochin 7 rows selected
同样,以下查询根据Employee : 的工资降序排列表的内容;
ij> SELECT * FROM Employees ORDER BY Salary DESC;
这将产生以下输出 :
ID |NAME |SALARY |LOCATION --------------------------------------------------------------- 3 |Renuka |50000 |Delhi 5 |Trupthi |45000 |Kochin 2 |Kalyan |40000 |Vishakhapatnam 7 |Rahul |39000 |Lucknow 6 |Suchatra |33000 |Pune 1 |Amit |30000 |Hyderabad 4 |Archana |15000 |Mumbai 7 rows selected
本节教你如何对a的内容进行排序Derby中的表使用JDBC.您可以使用ORDER BY子句和关键字ASC(表示升序)和DSC(表示降序)按顺序排列记录.
如果要使用Derby网络服务器请求网络客户端,确保服务器已启动并正在运行.网络客户端驱动程序的类名是org.apache.derby.jdbc.ClientDriver,URL是jdbc:derby://localhost:1527/ DATABASE_NAME; create = true; user = USER_NAME; passw
ord = PASSWORD ".
按照以下步骤对Apache Derby中的表记录进行排序 : 号;
要与数据库通信,首先需要注册驱动程序. forName()类的方法类接受表示类名的String值将其加载到内存中,自动注册它.使用此方法注册驱动程序.
通常,我们与数据库进行通信的第一步是连接它.连接类表示与数据库服务器的物理连接.您可以通过调用 DriverManager 类的 getConnection()方法来创建连接对象.使用此方法.
您需要创建语句或 PreparedStatement 或 CallableStatement 对象,用于将SQL语句发送到数据库.您可以分别使用方法 createStatement(),prepareStatement()和prepareCall()创建它们.使用适当的方法创建其中任何一个对象.
创建语句后,需要执行它. Statement 类提供了各种方法来执行查询,如 execute()方法,以执行返回多个结果集的语句. executeUpdate()方法执行INSERT,UPDATE,DELETE等查询. executeQuery()方法返回数据.使用这些方法之一并执行先前创建的语句.
以下JDBC示例演示如何在Apache Derby中对表的记录进行排序使用JDBC程序.在这里,我们使用嵌入式驱动程序连接到名为sampleDB的数据库(如果它不存在将创建).
import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; public class SortData { public static void main(String args[]) throws SQLException, ClassNotFoundException { //Registering the driver Class.forName("org.apache.derby.jdbc.EmbeddedDriver"); //Getting the Connection object String URL = "jdbc:derby:SampleDB;create=true"; Connection conn = DriverManager.getConnection(URL); //Creating the Statement object Statement stmt = conn.createStatement(); //Creating a table and populating it String query = "CREATE TABLE Employees(" + "Id INT NOT NULL GENERATED ALWAYS AS IDENTITY, " + "Name VARCHAR(255), Salary INT NOT NULL, " + "Location VARCHAR(255), " + "PRIMARY KEY (Id))"; String query = "INSERT INTO Employees(" + "Name, Salary, Location) VALUES " + "('Amit', 30000, 'Hyderabad'), " + "('Kalyan', 40000, 'Vishakhapatnam'), " + "('Renuka', 50000, 'Delhi'), " + "('Archana', 15000, 'Mumbai'), " + "('Trupthi', 45000, 'Kochin'), " + "('Suchatra', 33000, 'Pune'), " + "('Rahul', 39000, 'Lucknow'), " + "('Trupti', 45000, 'Kochin')"; //Executing the query String query = "SELECT Location, SUM(Salary) " + "from Employees GROUP BY Location"; ResultSet rs = stmt.executeQuery(query); while(rs.next()) { System.out.println("Salary: "+rs.getString(1)); System.out.println("Location: "+rs.getString(2)); System.out.println(" "); } } }
执行上述程序时,你将得到以下输出 :
Salary: Chennai Location: 43000 Salary: Delhi Location: 50000 Salary: Hyderabad Location: 30000 Salary: Kochin Location: 45000 Salary: Lucknow Location: 39000 Salary: Mumbai Location: 15000 Salary: Pune Location: 33000