Example of utilizing relationships to keep SOQL outside of a loop

gistfile1.txt

List<Account> accList = new List<Account>(
    [Select 
        Id
        ,Name
        ,(Select 
              Email
          From
              Contacts
        )
     From Account]
);
 
List<Account> accountsToUpdate = new List<Account>(); 
for(Account acc : accList){
    Integer numWithEmail = 0;
    for(Contact cont : acc.Contacts){
        if(!String.isEmpty(cont.Email)){
            numWithEmail++;
        }
    }
    acc.Contacts_With_Email_Address__c = numWithEmail;
    accountsToUpdate.add(acc);
}
update accountsToUpdate;