code: def downgrade():
      with op.batch_alter_table("dbs") as batch_op:
          batch_op.add_column(
              sa.Column("perm", sa.String(1000), nullable=True)
          )
  
imports: import sqlalchemy
  from alembic import op
label_desc: Use image node_id 2 for calling a global function with example usage: downgrade() without return types