INSERT, UPDATE, DELETE

SELECT queries read data and hand you back a ResultSet. INSERT, UPDATE, and DELETE are different — they change data instead of reading it, and JDBC gives you a separate method for that: Statement.executeUpdate(sql). This page covers all three write operations and how to confirm they actually did something.

executeUpdate() Returns a Row Count, Not a ResultSet

Any SQL statement that modifies data — INSERT, UPDATE, or DELETE — is run with executeUpdate(sql) instead of executeQuery(sql). It does not return a ResultSet because there are no rows to read back. Instead, it returns an int: the number of rows that were affected by the statement.

INSERT: Adding a New Row

An INSERT adds a brand-new row to a table. The row count returned is almost always 1 for a single-row insert.

import java.sql.*;

public class InsertExample {
  public static void main(String[] args) throws Exception {
    Connection conn = DriverManager.getConnection(
      "jdbc:mysql://localhost:3306/coding_with_sonu", "root", "");
    Statement stmt = conn.createStatement();

    String sql = "INSERT INTO students (name, course) VALUES ('Amit', 'JDBC')";
    int rowsInserted = stmt.executeUpdate(sql);

    System.out.println(rowsInserted + " row(s) inserted.");

stmt.close(); conn.close();
  }
}

UPDATE: Modifying Existing Rows

An UPDATE changes values in rows that already exist. The row count tells you how many rows matched the WHERE clause and were changed — this could be 0, 1, or many.

String sql = "UPDATE students SET course = 'Advanced JDBC' WHERE name = 'Amit'";
int rowsUpdated = stmt.executeUpdate(sql);

System.out.println(rowsUpdated + " row(s) updated.");

DELETE: Removing Rows

A DELETE removes rows that match a condition. Just like UPDATE, the row count tells you how many rows were actually removed.

String sql = "DELETE FROM students WHERE name = 'Amit'";
int rowsDeleted = stmt.executeUpdate(sql);

System.out.println(rowsDeleted + " row(s) deleted.");

Always Check the Row Count

The int returned by executeUpdate() is not just informational — it's how you know whether your statement actually matched anything. An UPDATE or DELETE with a WHERE clause that matches nothing will not throw an exception; it will simply return 0. If your code assumes the operation succeeded without checking this, you can silently miss bugs like a typo'd ID or a row that was already deleted.

String sql = "UPDATE students SET course = 'Advanced JDBC' WHERE name = 'Ghost'";
int rowsAffected = stmt.executeUpdate(sql);

if (rowsAffected == 0) {
  System.out.println("No matching row found - nothing was updated.");
} else {
  System.out.println(rowsAffected + " row(s) updated.");
}