What are the differences between execute, executeQuery, and executeUpdate methods in JDBC, and when should each be used?

In JDBC, the methods execute, executeQuery, and executeUpdate have different purposes:

• executeQuery() — used to execute SQL queries that return a result set (SELECT). Returns a ResultSet object.

• executeUpdate() — used to execute SQL commands that modify data or database structure (INSERT, UPDATE, DELETE, DDL). Returns the number of affected rows.

• execute() — a universal method that can execute any SQL statement. Returns a boolean: true if the result is a ResultSet, false if it is an update count.

When to use:

• For data retrieval — executeQuery.
• For data or structure modification — executeUpdate.
• If the query type is unknown in advance or can vary — execute.

Example:

String sql = "SELECT * FROM users";
ResultSet rs = statement.executeQuery(sql);

String updateSql = "UPDATE users SET name='John' WHERE id=1";
int rows = statement.executeUpdate(updateSql);

boolean hasResultSet = statement.execute(sql);
if (hasResultSet) {
    ResultSet rs2 = statement.getResultSet();
    // processing
}