code: def downgrade():
      bind = op.get_bind()
      insp = sa.engine.reflection.Inspector.from_engine(bind)
  
      # Add cluster_name column
      with op.batch_alter_table("datasources") as batch_op:
          batch_op.add_column(sa.Column("cluster_name", sa.String(250)))
  
      # Update cluster_name values
      metadata = sa.MetaData(bind=bind)
      datasources = sa.Table("datasources", metadata, autoload=True)
      clusters = sa.Table("clusters", metadata, autoload=True)
  
      statement = datasources.update().values(
          cluster_name=sa.select([clusters.c.cluster_name])
          .where(datasources.c.cluster_id == clusters.c.id)
          .as_scalar()
      )
      bind.execute(statement)
  
      with op.batch_alter_table("datasources") as batch_op:
          # Drop cluster_id column
          fk_constraint_name = generic_find_fk_constraint_name(
              "datasources", {"id"}, "clusters", insp
          )
          uq_constraint_name = generic_find_uq_constraint_name(
              "datasources", {"cluster_id", "datasource_name"}, insp
          )
          batch_op.drop_constraint(
              fk_constraint_name, type_="foreignkey"
          )
          batch_op.drop_constraint(uq_constraint_name, type_="unique")
          batch_op.drop_column("cluster_id")
  
          # Add constraints to cluster_name column
          batch_op.alter_column(
              "cluster_name",
              existing_type=sa.String(250),
              nullable=False,
          )
          batch_op.create_unique_constraint(
              "uq_datasources_cluster_name",
              ["cluster_name", "datasource_name"],
          )
          batch_op.create_foreign_key(
              "fk_datasources_cluster_name_clusters",
              "clusters",
              ["cluster_name"],
              ["cluster_name"],
          )
  
imports: import sqlalchemy
  from alembic import op
  from superset import db
  from superset.utils.core import generic_find_fk_constraint_name, generic_find_uq_constraint_name
label_desc: Use image node_id 2 for calling a global function with example usage: downgrade() without return types