input: Write a function to generate a SQL query string.
  assert generate_sql_query("employees", ["name", "position", "salary"], "salary > 50000") == "SELECT name, position, salary FROM employees WHERE salary > 50000"
  assert generate_sql_query("students", ["id", "name", "grade"], "grade > 3.5") == "SELECT id, name, grade FROM students WHERE grade > 3.5"
  assert generate_sql_query("products", ["product_id", "product_name", "price"], "price < 20") == "SELECT product_id, product_name, price FROM products WHERE price < 20"
output: def generate_sql_query(table_name, columns, condition):
      columns_str = ", ".join(columns)
      return f"SELECT {columns_str} FROM {table_name} WHERE {condition}"