DELETE语句用于删除表的行.与UPDATE语句一样,Apache Derby提供两种类型的Delete(语法):搜索删除和定位删除.
搜索delete语句删除表的所有指定列.
DELETE语句的语法如下 :
ij> DELETE FROM table_name WHERE condition;
我们假设我们有一个名为employee的表,其中包含5条记录,如下所示 :
ID |NAME |SALARY |LOCATION ---------------------------------------------------------------------------- 1 |Amit |30000 |Hyderabad 2 |Kalyan |40000 |Vishakhapatnam 3 |Renuka |50000 |Delhi 4 |Archana |15000 |Mumbai 5 |Trupti |45000 |Kochin 5 rows selected
以下SQL DELETE语句删除名为Trupti的记录.
ij> DELETE FROM Employees WHERE Name = 'Trupti'; 1 row inserted/updated/deleted
如果获得Employees表的内容,则只能看到如下所示的四条记录和减号;
ID |NAME |SALARY |LOCATION ---------------------------------------------------------------------------- 1 |Amit |30000 |Hyderabad 2 |Kalyan |40000 |Vishakhapatnam 3 |Renuka |50000 |Delhi 4 |Archana |15000 |Mumbai 4 rows selected
要删除表中的所有记录,请执行不带where子句的相同查询.
ij> DELETE FROM Employees; 4 rows inserted/updated/deleted
现在,如果您尝试获取Employee表的内容,您将获得一个空表给出以下 :
ij> select * from employees; ID |NAME |SALARY |LOCATION -------------------------------------------------------- 0 rows selected
本节介绍如何使用JDBC应用程序删除Apache Derby数据库中表的现有记录.
如果要请求Derby使用网络客户端的网络服务器,确保服务器已启动并运行.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 ".
按照以下步骤删除Apache Derby中表格的现有记录:/p>
首先,您需要注册驱动程序以与数据库通信. forName()类类的方法接受表示类名的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.创建连接使用此方法离子.
您需要创建语句或 PreparedStatement或CallableStatement 对象将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()方法返回数据的结果.使用这些方法之一并执行先前创建的语句.
以下JDBC示例演示如何删除Apache中表的现有记录Derby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.SQLException; import java.sql.Statement; public class DeleteData { public static void main(String args[]) throws Exception { //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'), " + "('Trupthi', 45000, 'Kochin')"; //Executing the query String query = "DELETE FROM Employees WHERE Name = 'Trupthi'"; int num = stmt.executeUpdate(query); System.out.println("Number of records deleted are: "+num); } }
执行上述程序后,您将获得以下输出 :
Number of records deleted are: 1