Method selected_columns

lib/sqlalchemy/sql/selectable.py:6751–6826

A :class:`_expression.ColumnCollection` representing the columns that this SELECT statement or similar construct returns in its result set, not including :class:`_sql.TextClause` constructs. This collection differs from the :attr:`_expression.FromClause.columns`

(
        self,
    )

    @HasMemoized_ro_memoized_attribute
    def selected_columns(
        self,
    ) -> ColumnCollection[str, ColumnElement[Any]]:
        """A :class:`_expression.ColumnCollection`
        representing the columns that
        this SELECT statement or similar construct returns in its result set,
        not including :class:`_sql.TextClause` constructs.

        This collection differs from the :attr:`_expression.FromClause.columns`
        collection of a :class:`_expression.FromClause` in that the columns
        within this collection cannot be directly nested inside another SELECT
        statement; a subquery must be applied first which provides for the
        necessary parenthesization required by SQL.

        For a :func:`_expression.select` construct, the collection here is
        exactly what would be rendered inside the "SELECT" statement, and the
        :class:`_expression.ColumnElement` objects are directly present as they
        were given, e.g.::

            col1 = column("q", Integer)
            col2 = column("p", Integer)
            stmt = select(col1, col2)

        Above, ``stmt.selected_columns`` would be a collection that contains
        the ``col1`` and ``col2`` objects directly. For a statement that is
        against a :class:`_schema.Table` or other
        :class:`_expression.FromClause`, the collection will use the
        :class:`_expression.ColumnElement` objects that are in the
        :attr:`_expression.FromClause.c` collection of the from element.

        A use case for the :attr:`_sql.Select.selected_columns` collection is
        to allow the existing columns to be referenced when adding additional
        criteria, e.g.::

            def filter_on_id(my_select, id):
                return my_select.where(my_select.selected_columns["id"] == id)


            stmt = select(MyModel)

            # adds "WHERE id=:param" to the statement
            stmt = filter_on_id(stmt, 42)

        .. note::

            The :attr:`_sql.Select.selected_columns` collection does not
            include expressions established in the columns clause using the
            :func:`_sql.text` construct; these are silently omitted from the
            collection. To use plain textual column expressions inside of a
            :class:`_sql.Select` construct, use the :func:`_sql.literal_column`
            construct.


        .. versionadded:: 1.4

        """

        # compare to SelectState._generate_columns_plus_names, which