Method visit_textual_select

lib/sqlalchemy/sql/compiler.py:2809–2861

(
        self, taf, compound_index=None, asfrom=False, **kw
    )

        return "".join(self.process(part, **kw) for part in tstring.parts)

    def visit_textual_select(
        self, taf, compound_index=None, asfrom=False, **kw
    ):
        if self._collect_params:
            self._add_to_params(taf)
        toplevel = not self.stack
        entry = self._default_stack_entry if toplevel else self.stack[-1]

        new_entry: _CompilerStackEntry = {
            "correlate_froms": set(),
            "asfrom_froms": set(),
            "selectable": taf,
        }
        self.stack.append(new_entry)

        if taf._independent_ctes:
            self._dispatch_independent_ctes(taf, kw)

        populate_result_map = (
            toplevel
            or (
                compound_index == 0
                and entry.get("need_result_map_for_compound", False)
            )
            or entry.get("need_result_map_for_nested", False)
        )

        if populate_result_map:
            self._ordered_columns = self._textual_ordered_columns = (
                taf.positional
            )

            # enable looser result column matching when the SQL text links to
            # Column objects by name only
            self._loose_column_name_matching = not taf.positional and bool(
                taf.column_args
            )

            for c in taf.column_args:
                self.process(
                    c,
                    within_columns_clause=True,
                    add_to_result_map=self._add_to_result_map,
                )

        text = self.process(taf.element, **kw)
        if self.ctes:
            nesting_level = len(self.stack) if not toplevel else None
            text = self._render_cte_clause(nesting_level=nesting_level) + text

        self.stack.pop(-1)

        return text

    def visit_null(self, expr: Null, **kw: Any) -> str:
        return "NULL"