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JDBC CRUD Query
Once you have successfully established a JDBC connection, you can execute SQL queries (SELECT, INSERT, UPDATE, DELETE) using Statement or PreparedStatement.
Fetch Data from Database (SELECT):
🔹 executeQuery() → Used for SELECT queries (returns ResultSet).
🔹 ResultSet → Stores the retrieved data from the database.
🔹 rs.next() → Moves to the next row in the result set.
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class JDBCSelectExample {
public static void main(String[] args) {
String url = "jdbc:mysql://localhost:3306/mydb";
String user = "root";
String password = "password";
try (Connection con = DriverManager.getConnection(url, user, password);
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery("SELECT * FROM employees")) {
while (rs.next()) {
int id = rs.getInt("id");
String name = rs.getString("name");
String role = rs.getString("role");
System.out.println("ID: " + id + ", Name: " + name + ", Role: " + role);
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
Inserting Data using PreparedStatement:
🔹 executeUpdate() → Used for INSERT, UPDATE, DELETE (returns affected row count).
🔹 pstmt.setString(1, "John Doe") → Sets the first placeholder (?).
🔹 pstmt.setString(2, "Manager") → Sets the second placeholder (?).
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
public class JDBCInsertExample {
public static void main(String[] args) {
String url = "jdbc:mysql://localhost:3306/mydb";
String user = "root";
String password = "password";
String sql = "INSERT INTO employees (name, role) VALUES (?, ?)";
try (Connection con = DriverManager.getConnection(url, user, password);
PreparedStatement pstmt = con.prepareStatement(sql)) {
pstmt.setString(1, "John Doe"); // First parameter
pstmt.setString(2, "Manager"); // Second parameter
int rowsInserted = pstmt.executeUpdate(); // Execute query
if (rowsInserted > 0) {
System.out.println("✅ Data inserted successfully!");
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
Updating Data using PreparedStatement:
String sql = "UPDATE employees SET role = ? WHERE id = ?";
try (PreparedStatement pstmt = con.prepareStatement(sql)) {
pstmt.setString(1, "Senior Developer");
pstmt.setInt(2, 101); // Employee ID
int rowsUpdated = pstmt.executeUpdate();
if (rowsUpdated > 0) {
System.out.println("✅ Employee role updated successfully!");
}
}
Deleting Data using PreparedStatement:
String sql = "DELETE FROM employees WHERE id = ?";
try (PreparedStatement pstmt = con.prepareStatement(sql)) {
pstmt.setInt(1, 101); // Employee ID to delete
int rowsDeleted = pstmt.executeUpdate();
if (rowsDeleted > 0) {
System.out.println("✅ Employee deleted successfully!");
}
}