global class UpdateAccountCloseDealAmount implements Database.Batchable<sObject> {
    global Database.QueryLocator start(Database.BatchableContext BC) {
        return Database.getQueryLocator('SELECT Id, CloseDealAmount__c, (SELECT Amount FROM Opportunities WHERE StageName = \'Closed Won\') FROM Account');
    }
    
    global void execute(Database.BatchableContext BC, List<Account> scope) {
        for(Account acc : scope) {
            Decimal maxAmount = 0;
            for(Opportunity opp : acc.Opportunities) {
                if(opp.Amount > maxAmount) {
                    maxAmount = opp.Amount;
                }
            }
            acc.CloseDealAmount__c = maxAmount;
        }
        update scope;
    }
    
    global void finish(Database.BatchableContext BC) {}
}