The aggregate functions COUNT(fieldname), COUNT_DISTINCT(), SUM(), AVG(), MIN() and MAX() in SOQL return an AggregateResult object or a List of AggregateResult objects. We can use aggregate functions result in apex by using AggregateResult object.

Here is an example to use AggregateResult in Salesforce. In below example I’m using COUNT(fieldname) aggregate function in SOQL to show Account record respective number of Contacts.

Visualforce Page:

<apex:page controller="SampleController" action="{!getData}">
    <apex:form >
        <apex:pageBlock >
            <apex:pageblockTable value="{!accWrapList}" var="acc">            
                <apex:column headerValue="Account Name" value="{!acc.AccountName}"/>
                <apex:column headerValue="Number of Contacts" value="{!acc.TotalContact}"/>
            </apex:pageblockTable>
        </apex:pageBlock>
    </apex:form>
</apex:page>

Apex Class:

public with sharing class SampleController {
    public List<AggregateResult> result {get;set;}    
    public List<AccWrapper> accWrapList {get;set;}
    public List<Account> accList;
    public Map<Id, Account> accMap;
    List<Id> idList;
    
    public void getData() {
        accWrapList = new List<AccWrapper>();
        result = new List<AggregateResult>();
        idList = new List<Id>();
        accList = new List<Account>();
        accMap = new Map<Id, Account>();
        
        result = [SELECT COUNT(Id) Total, AccountId FROM Contact WHERE AccountId != null GROUP BY AccountId];               
        
        for(AggregateResult a : Result) {   
            idList.add((Id)a.get('AccountId'));
        }
        
        accList = [SELECT Id, Name FROM Account WHERE Id IN : idList];
        for(Account a : accList) {
            accMap.put(a.Id, a);            
        }
        
        for(AggregateResult aResult : result) {
            Account acc = accMap.get((Id)(aResult.get('AccountId')));
            accWrapList.add(new AccWrapper(aResult, acc.Name)); 
        }
    }
    
    public class AccWrapper {
        public Integer TotalContact {get;set;}
        public String AccountName {get;set;}
        
        public AccWrapper(AggregateResult a, String AccountName) {
            this.TotalContact =  (Integer)a.get('Total');
            this.AccountName = AccountName;
        }
    }
}

Output: