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-
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)。
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);
</span><span class="com">//获取Statement对象</span><span class="pln">
</span><span class="typ">Statement</span><span class="pln"> stmt</span><span class="pun">=</span><span class="pln">conn</span><span class="pun">.</span><span class="pln">createStatement</span><span class="pun">();</span><span class="pln">
</span><span class="com">//创建表结构,插入一些测试数据</span><span class="pln">
</span><span class="typ">String</span><span class="pln"> query</span><span class="pun">=</span><span class="str">"CREATE TABLE Employees("</span><span class="pln">
</span><span class="pun">+</span><span class="pln"> </span><span class="str">"Id INT NOT NULL GENERATED ALWAYS AS IDENTITY, "</span><span class="pln">
</span><span class="pun">+</span><span class="pln"> </span><span class="str">"Name VARCHAR(255), Salary INT NOT NULL, "</span><span class="pln">
</span><span class="pun">+</span><span class="pln"> </span><span class="str">"Location VARCHAR(255), "</span><span class="pln">
</span><span class="pun">+</span><span class="pln"> </span><span class="str">"PRIMARY KEY (Id))"</span><span class="pun">;</span><span class="pln">
</span><span class="typ">String</span><span class="pln"> query</span><span class="pun">=</span><span class="str">"INSERT INTO Employees("</span><span class="pln">
</span><span class="pun">+</span><span class="pln"> </span><span class="str">"Name, Salary, Location) VALUES "</span><span class="pln">
</span><span class="pun">+</span><span class="pln"> </span><span class="str">"(Amit, 30000, Hyderabad), "</span><span class="pln">
</span><span class="pun">+</span><span class="pln"> </span><span class="str">"(Kalyan, 40000, Vishakhapatnam), "</span><span class="pln">
</span><span class="pun">+</span><span class="pln"> </span><span class="str">"(Renuka, 50000, Delhi), "</span><span class="pln">
</span><span class="pun">+</span><span class="pln"> </span><span class="str">"(Learnfk, 15000, Mumbai), "</span><span class="pln">
</span><span class="pun">+</span><span class="pln"> </span><span class="str">"(Trupthi, 45000, Kochin), "</span><span class="pln">
</span><span class="pun">+</span><span class="pln"> </span><span class="str">"(Suchatra, 33000, Pune), "</span><span class="pln">
</span><span class="pun">+</span><span class="pln"> </span><span class="str">"(Rahul, 39000, Lucknow), "</span><span class="pln">
</span><span class="pun">+</span><span class="pln"> </span><span class="str">"(Trupthi, 45000, Kochin)"</span><span class="pun">;</span><span class="pln">
</span><span class="com">//执行SQL语句</span><span class="pln">
</span><span class="typ">String</span><span class="pln"> query</span><span class="pun">=</span><span class="str">"DELETE FROM Employees WHERE Name=Trupthi"</span><span class="pun">;</span><span class="pln">
</span><span class="kwd">int</span><span class="pln"> num</span><span class="pun">=</span><span class="pln">stmt</span><span class="pun">.</span><span class="pln">executeUpdate</span><span class="pun">(</span><span class="pln">query</span><span class="pun">);</span><span class="pln">
</span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Number of records deleted are: "</span><span class="pun">+</span><span class="pln">num</span><span class="pun">);</span><span class="pln">
}
}
在执行上述程序时，您将获得以下输出-
Number of records deleted are: 1
