def _table_column(t, expr): op = expr.op() ctx = t.context table = op.table sa_table = _get_sqla_table(ctx, table) out_expr = getattr(sa_table.c, op.name) expr_type = expr.type() if isinstance(expr_type, dt.Timestamp): timezone = expr_type.timezone if timezone is not None: out_expr = out_expr.op('AT TIME ZONE')(timezone).label(op.name) # If the column does not originate from the table set in the current SELECT # context, we should format as a subquery if t.permit_subquery and ctx.is_foreign_expr(table): return sa.select([out_expr]) return out_expr