Statement 类作用 :
int executeUpdate(String sql) throws SQLException;
ResultSet executeQuery(String sql) throws SQLException;
三种 SQL 语句说明 :
// 增加数据
INSERT INTO user (name, age, email) VALUES ('John', 25, 'john@example.com');
// 删除数据
DELETE FROM user WHERE age < 18;
// 修改数据
UPDATE user SET age = 26 WHERE name = 'John';
// 创建数据库
CREATE TABLE user (
id INT PRIMARY KEY,
name VARCHAR(20),
age INT,
email VARCHAR(50)
);
// 修改数据库表字段
ALTER TABLE user ADD COLUMN phone VARCHAR(20);
// 删除数据库表
DROP TABLE user;
SELECT * FROM user WHERE age > 18;
下面的示例是执行 DQL 查询语句的代码 ;
代码示例 :
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
try {
conn = DriverManager.getConnection(url, username, password);
stmt = conn.createStatement();
String sql = "SELECT * FROM user";
rs = stmt.executeQuery(sql);
while (rs.next()) {
int id = rs.getInt("id");
String name = rs.getString("name");
int age = rs.getInt("age");
System.out.println("id: " + id + ", name: " + name + ", age: " + age);
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (rs != null) {
try {
rs.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (stmt != null) {
try {
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (conn != null) {
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}