How do you retrieve auto-generated keys after an INSERT in JDBC? JDBC में INSERT के बाद auto-generated keys कैसे retrieve करें?

When inserting a row into a table with an auto-increment primary key, JDBC lets you retrieve that generated key immediately using RETURN_GENERATED_KEYS, avoiding a separate SELECT query.

String sql = 'INSERT INTO users (name, email) VALUES (?, ?)';

// Request generated keys when preparing the statement
PreparedStatement pstmt = conn.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS);
pstmt.setString(1, 'John');
pstmt.setString(2, 'john@example.com');

int affectedRows = pstmt.executeUpdate();

if (affectedRows > 0) {
    try (ResultSet generatedKeys = pstmt.getGeneratedKeys()) {
        if (generatedKeys.next()) {
            long newId = generatedKeys.getLong(1);  // the auto-generated primary key
            System.out.println('New user ID: ' + newId);
        }
    }
}

// Alternative: specifying which column names to retrieve (some drivers require this)
PreparedStatement pstmt2 = conn.prepareStatement(sql, new String[]{'id'});

// Common use case: inserting a parent row, then using its generated ID
// for a related child row insert within the same transaction
conn.setAutoCommit(false);
try {
    long orderId;
    PreparedStatement orderStmt = conn.prepareStatement(
        'INSERT INTO orders (customer_id) VALUES (?)', Statement.RETURN_GENERATED_KEYS);
    orderStmt.setInt(1, customerId);
    orderStmt.executeUpdate();
    try (ResultSet keys = orderStmt.getGeneratedKeys()) {
        keys.next();
        orderId = keys.getLong(1);
    }

    PreparedStatement itemStmt = conn.prepareStatement(
        'INSERT INTO order_items (order_id, product) VALUES (?, ?)');
    itemStmt.setLong(1, orderId);
    itemStmt.setString(2, 'Widget');
    itemStmt.executeUpdate();

    conn.commit();
} catch (SQLException e) {
    conn.rollback();
}