code: def mssql_get_pk_index_name(engine: Engine,
                              tablename: str,
                              schemaname: str = MSSQL_DEFAULT_SCHEMA) -> str:
      
      # http://docs.sqlalchemy.org/en/latest/core/connections.html#sqlalchemy.engine.Connection.execute  # noqa
      # http://docs.sqlalchemy.org/en/latest/core/sqlelement.html#sqlalchemy.sql.expression.text  # noqa
      # http://docs.sqlalchemy.org/en/latest/core/sqlelement.html#sqlalchemy.sql.expression.TextClause.bindparams  # noqa
      # http://docs.sqlalchemy.org/en/latest/core/connections.html#sqlalchemy.engine.ResultProxy  # noqa
      query = text("""
  SELECT
      kc.name AS index_name
  FROM
      sys.key_constraints AS kc
      INNER JOIN sys.tables AS ta ON ta.object_id = kc.parent_object_id
      INNER JOIN sys.schemas AS s ON ta.schema_id = s.schema_id
  WHERE
      kc.[type] = 'PK'
      AND ta.name = :tablename
      AND s.name = :schemaname
      """).bindparams(
          tablename=tablename,
          schemaname=schemaname,
      )
      with contextlib.closing(
              engine.execute(query)) as result:  # type: ResultProxy  # noqa
          row = result.fetchone()
          return row[0] if row else ''
docs: For Microsoft SQL Server specifically: fetch the name of the PK index
      for the specified table (in the specified schema), or ``''`` if none is
      found.