code: def upgrade():
      """Apply Add ``timetable_description`` column to DagModel for UI."""
      with op.batch_alter_table("dag", schema=None) as batch_op:
          batch_op.add_column(
              sa.Column(
                  "timetable_description",
                  sa.String(length=1000),
                  nullable=True,
              )
          )
  
imports: from __future__ import annotations
  import sqlalchemy
  from alembic import op
label_desc: Use image node_id 1 for calling a global function with example usage: upgrade() without return types