THIS IS WHAT I HAVE:

Object:  Stock

Assuming that after stock keeper has entered some records; he discovers that he erroneously entered an incorrect Qty Sold for record three (which reads 8 instead of 5) and he decides to update.

WHAT I WANT TO ACHIEVE:

A bulk Trigger to update the two Later (Upper) records immediately after stock keeper updates Qty Sold for record three from 8 to 5.

Logic: add the difference b/w the Old Qty Sold and New Qty Sold (i.e. 8 - 5 = 3) to the Qty Left of the two Later  (Upper) records.

This will display the accurate information about the stock table as shown below:

TRIGGER CODE:

trigger stockKeeping on Stock__c (after Update) {
    
    Map<String, Stock__c> stockMap = new Map<String, Stock__c>();
   
    Decimal val = 0;
    String oldName = '';

    for(Stock__c stock: System.Trigger.new) {

        oldName = System.Trigger.oldMap.get(stock.Id).Name;

        if(stock.Name == oldName){
            val = stock.Qty_Sold__c - System.Trigger.oldMap.get(stock.Id).Qty_Sold__c;
            stockMap.put(stock.Name, stock);
        }
    }
    
    List<Stock__c> listStock = [SELECT Id, Name, Stock__c, Qty_Sold__c, Date__c FROM Stock__c WHERE Name NOT IN     :stockMap.KeySet() ORDER BY Date__c DESC];
    
    for (Stock__c stock: listStock) {
       
       if(ock.Date__c > stockMap.get(oldName).Date__c ) {
            stock.Stock__c += val;            
       }                    
    }
    
    update listStock;        //line 25, column 5
}

ERROR: 

Invalid Data.
stockKeeping: execution of AfterUpdate caused by: System.DmlException: Update failed.
First exception on row 0 with id a06U0000004prYrIAI; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, stockKeeping: maximum trigger depth exceeded Stock trigger event AfterUpdate for [a06U0000000vSLy] Stock trigger event AfterUpdate for [a06U0000000vSLt, a06U0000000vSM3, a06U0000004prYr] Stock trigger event AfterUpdate for [a06U0000000vSLy] Test trigger event AfterUpdate for [a06U0000000vSLt, a06U0000000vSM3, a06U0000004prYr] Stock trigger event AfterUpdate for [a06U0000000vSLy] Stock trigger event AfterUpdate for [a06U0000000vSLt, a06U0000000vSM3, a06U0000004prYr] Stock trigger event AfterUpdate for [a06U0000000vSLy] Stock trigger event AfterUpdate for [a06U0000000vSLt, a06U0000000vSM3, a06U0000004prYr] Stock trigger event AfterUpdate for [a06U0000000vSLy] Stock trigger event AfterUpdate for [a06U0000000vSLt, a06U0000000vSM3, a06U0000004prYr] Stock trigger event AfterUpdate for [a06U0000000vSLy] Stock trigger event AfterUpdate for [a06U0000000vSLt, a06U0000000vSM3, a06U0000004prYr] Stock trigger event AfterUpdate for [a06U0000000vSLy] Stock trigger event AfterUpdate for [a06U0000000vSLt, a06U0000000vSM3, a06U0000004prYr] Stock trigger event AfterUpdate for [a06U0000000vSLy] Stock trigger event AfterUpdate for [a06U0000000vSLt, a06U0000000vSM3, a06U0000004prYr]: []: Trigger.stockKeeping: line 25, column 5

Please can somebody help!!.

Thanks.