What is the difference between the execute, executeQuery, and executeUpdate methods?

executeQuery is used to execute SELECT queries and returns a ResultSet object with the results.

executeUpdate is used for executing DML commands (INSERT, UPDATE, DELETE) or DDL commands (CREATE, ALTER, DROP). It returns the number of affected rows.

execute can execute any type of SQL command. It returns a boolean: true if the result is a ResultSet, and false otherwise (if it is an update count or no result). To get the ResultSet, use getResultSet(), and to get the update count, use getUpdateCount().

Method	Purpose	Return Type	Example SQL Commands
executeQuery	SELECT	ResultSet	SELECT * FROM users
executeUpdate	INSERT, UPDATE, DELETE, DDL	int (rows affected)	INSERT INTO users ..., UPDATE users ..., DROP TABLE users
execute	Any type	boolean	Any SQL command

Example of using executeQuery:

// Getting connection
Connection conn = ...;
Statement stmt = conn.createStatement();
// Executing SELECT
ResultSet rs = stmt.executeQuery("SELECT id, name FROM users");
while (rs.next()) {
    int id = rs.getInt("id");
    String name = rs.getString("name");
    System.out.println("ID: " + id + ", Name: " + name);
}
rs.close();
stmt.close();
conn.close();

Example of using executeUpdate:

// Getting connection
Connection conn = ...;
Statement stmt = conn.createStatement();
// Executing INSERT
int updatedRows = stmt.executeUpdate("INSERT INTO users (name) VALUES ('John Doe')");
System.out.println("Inserted rows: " + updatedRows);
stmt.close();
conn.close();

Example of using execute:

// Getting connection
Connection conn = ...;
Statement stmt = conn.createStatement();
// Executing DDL
boolean isResultSet = stmt.execute("CREATE TABLE products (id INT PRIMARY KEY, name VARCHAR(255))");
if (!isResultSet) {
    System.out.println("Table created or updated count: " + stmt.getUpdateCount());
}
stmt.close();
conn.close();