from typing import List


def _build_not_null_string(column_names: List[str]) -> str:
  """Construct NOT NULL condition

  Args:
      column_names: (List[string]), names of column

  Returns:
      string
  """
  not_null_string = ' AND '.join(
      ['{} IS NOT NULL'.format(cat) for cat in column_names])
  return not_null_string