code: def _downgrade_v4(op):
      
      op.drop_index('ix_equities_fuzzy_symbol')
      op.drop_index('ix_equities_company_symbol')
  
      op.execute("UPDATE equities SET exchange = exchange_full")
  
      with op.batch_alter_table('equities') as batch_op:
          batch_op.drop_column('exchange_full')
  
      op.create_index('ix_equities_fuzzy_symbol',
                      table_name='equities',
                      columns=['fuzzy_symbol'])
      op.create_index('ix_equities_company_symbol',
                      table_name='equities',
                      columns=['company_symbol'])
docs: Downgrades assets db by copying the `exchange_full` column to `exchange`,
      then dropping the `exchange_full` column.