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Derby - 删除数据

DELETE语句用于删除表的行数据。

Delete Data - 语法

DELETE语句的语法如下-

ij> DELETE FROM table_name WHERE condition;

Delete Data - 命令行示例

让无涯教程假设无涯教程有一个名为employee的表，其中包含5条记录，如下所示-

无涯教程网

ID |NAME |SALARY |LOCATION
----------------------------------------------------------------------------
1 |Amit |30000 |Hyderabad
2 |Kalyan |40000 |Vishakhapatnam
3 |Renuka |50000 |Delhi
4 |Learnfk |15000 |Mumbai
5 |Trupti |45000 |Kochin
5 rows selected

以下SQL DELETE语句删除名称为Trupti的记录。

ij> DELETE FROM Employees WHERE Name='Trupti';
1 row inserted/updated/deleted

如果获取Employees表的内容，则只能看到四个记录，如下所示-

ID |NAME |SALARY |LOCATION
----------------------------------------------------------------------------
1 |Amit |30000 |Hyderabad
2 |Kalyan |40000 |Vishakhapatnam
3 |Renuka |50000 |Delhi
4 |Learnfk |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，则会得到一个空表，如下所示-

ij> select * from employees;
ID |NAME |SALARY |LOCATION
--------------------------------------------------------
0 rows selected

Delete Data - JDBC示例

以下JDBC示例演示了如何使用JDBC程序删除Apache Derby中表的现有记录，在这里，无涯教程使用嵌入式驱动程序连接到名为sampleDB的数据库(如果不存在则创建)。

链接：https://www.learnfk.comhttps://www.learnfk.com/derby/apache-derby-delete-data.html

来源：LearnFk无涯教程网

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 {
      //注册驱动
      Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
      //创建连接
      String URL="jdbc:derby:sampleDB;create=true";
      Connection conn=DriverManager.getConnection(URL);

      //获取Statement对象
      Statement stmt=conn.createStatement();
      //创建表结构,插入一些测试数据
      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'), "
         + "('Learnfk', 15000, 'Mumbai'), "
         + "('Trupthi', 45000, 'Kochin'), "
         + "('Suchatra', 33000, 'Pune'), "
         + "('Rahul', 39000, 'Lucknow'), "
         + "('Trupthi', 45000, 'Kochin')";
      //执行SQL语句
      String query="DELETE FROM Employees WHERE Name='Trupthi'";
      int num=stmt.executeUpdate(query);
      System.out.println("Number of records deleted are: "+num);
   }
}