Two Effective Ways to Grab the Last Inserted Row's Value in Java with PostgreSQL

This method leverages PostgreSQL's built-in functionality to retrieve the desired value directly within the insert statement.

Example:

// Assuming your table has an auto-incrementing ID named "id"
String sql = "INSERT INTO your_table (column1, column2) VALUES (?, ?) RETURNING id;";

try (Connection conn = DriverManager.getConnection(connectionString);
     PreparedStatement ps = conn.prepareStatement(sql)) {
  ps.setString(1, "value1");
  ps.setString(2, "value2");
  
  // Execute the insert and retrieve the generated ID
  ResultSet rs = ps.executeQuery();
  if (rs.next()) {
    int lastInsertedId = rs.getInt("id");
    System.out.println("Last inserted ID: " + lastInsertedId);
  } else {
    System.out.println("No rows inserted.");
  }
} catch (SQLException e) {
  e.printStackTrace();
}

Explanation:

1. The RETURNING id clause appended to the INSERT statement specifies that the value of the "id" column should be returned after the insert operation.
2. The PreparedStatement is used to prevent SQL injection vulnerabilities.
3. After executing the query with executeQuery(), a ResultSet is obtained, containing the retrieved value.
4. We check if a row was inserted using next() and then access the "id" value using getInt("id").

Using getGeneratedKeys():

This method involves executing the insert statement separately and then using JDBC to retrieve the generated keys.

String sql = "INSERT INTO your_table (column1, column2) VALUES (?, ?);";

try (Connection conn = DriverManager.getConnection(connectionString);
     PreparedStatement ps = conn.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS)) {
  ps.setString(1, "value1");
  ps.setString(2, "value2");
  
  // Execute the insert
  ps.executeUpdate();
  
  // Retrieve the generated key
  ResultSet rs = ps.getGeneratedKeys();
  if (rs.next()) {
    int lastInsertedId = rs.getInt(1); // Assuming the key is the first column
    System.out.println("Last inserted ID: " + lastInsertedId);
  } else {
    System.out.println("No rows inserted.");
  }
} catch (SQLException e) {
  e.printStackTrace();
}

1. The Statement.RETURN_GENERATED_KEYS flag is set during statement creation, indicating that we want to retrieve the generated keys.
2. After executing the insert with executeUpdate(), the getGeneratedKeys() method is called to obtain a ResultSet containing the generated keys.
3. We check for rows and then access the first column (assuming the key is the first) using getInt(1).

Related Issues and Solutions:

• Incorrect column name: Ensure the column name specified in the RETURNING clause or accessed in getGeneratedKeys() matches the actual name of the auto-incrementing column.
• Multiple inserted rows: These methods only retrieve the value from the last inserted row. If you need all inserted values, consider using a SELECT statement after the insert.