code: def downgrade():
      op.drop_column("tables", "is_sqllab_view")
  
file_path: superset/superset/migrations/versions/2018-04-03_08-19_130915240929_is_sqllab_viz_flow.py
imports: import sqlalchemy
  from alembic import op
  from sqlalchemy.ext.declarative import declarative_base
  from superset import db
label_desc: Use image node_id 2 for calling a global function with example usage: downgrade() without return types