execute block returns( . . . )  
as                                                                         
   declare v_linked_client_order smallint;                                 
begin                                                                      
    if ( exists( select * from v_qdistr_avl_res ) ) then                 
    begin                                                                  
      v_linked_client_order = iif( rand() > 0.2, null, -1 );            
      select min(p.doc_list_id), min(client_order_id), count(*),        
             sum(p.purchase), sum(p.retail)                              
      from sp_customer_reserve( :v_linked_client_order ) p                
      into reserve_doc_id, client_order_id, total_lines, purchase_sum, retail_sum;       
      suspend;                                                             
   end                                                                     
end
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
PLAN (V_QDISTR_AVL_RES Q INDEX (QDISTR_RCV_ID))
PLAN (P NATURAL)
0 records fetched
   17663 ms , 42 write(s), 1032735 fetch(es), 292 mark(s)

Table                             Natural     Index    Update    Insert    Delete   Backout     Purge   Expunge
***************************************************************************************************************
RDB$INDICES                                       1                                                            
RDB$EXCEPTIONS                                    1                                                            
TMP$SHOPPING_CART                       5       716         6         2                   2                    
ZTMP_SHOPPING_CART                                                    4                                        
FIFO_RULES                             56       357                                                            
QDISTR                             231795     12321        28                                                  
ABEND_LOG                                                            28                                        
PERF_LOG                                          2         2         2