'Return the statement to create an index with varchar operator pattern
when the column type is \'varchar\' or \'text\', otherwise return None.'

def _create_like_index_sql(self, model, field):

    db_type = field.db_type(connection=self.connection)
    if ((db_type is not None) and (field.db_index or field.unique)):
        if ('[' in db_type):
            return None
        if db_type.startswith('varchar'):
            return self._create_index_sql(model, [field], suffix='_like', sql=self.sql_create_varchar_index)
        elif db_type.startswith('text'):
            return self._create_index_sql(model, [field], suffix='_like', sql=self.sql_create_text_index)
    return None
