code: def downgrade():
      # The following operation doesn't work on MySQL due to a foreign key constraint.
      #
      # mysql> DROP INDEX ix_trials_study_id ON trials;
      # ERROR: Cannot drop index 'ix_trials_study_id': needed in a foreign key constraint.
      op.drop_index(op.f("trials_study_id_key"), table_name="trials")
  
label_desc: Use image node_id 2 for calling a global function with example usage: downgrade() without return types