docs: def _relation_exists(cls, connection, relation):
          """ Returns True if relation exists in the postgres db. Otherwise returns False.
  
          Args:
              connection: connection to postgres database who stores mpr data.
              relation (str): name of the table, view or materialized view.
  
          Note:
              relation means table, view or materialized view here.
  
          Returns:
              boolean: True if relation exists, False otherwise.
  
          """
          schema_name, table_name = relation.split('.')
  
          exists_query = '''
              SELECT 1
              FROM   pg_catalog.pg_class c
              JOIN   pg_catalog.pg_namespace n ON n.oid = c.relnamespace
              WHERE  n.nspname = %s
              AND    c.relname = %s
              AND    (c.relkind = 'r' OR c.relkind = 'v' OR c.relkind = 'm')
                  -- r - table, v - view, m - materialized view.
          '''
          with connection.cursor() as cursor:
              cursor.execute(exists_query, [schema_name, table_name])
              result = cursor.fetchall()
              return result == [(1,)]