How to Aggregate using Database.query()?

We can use Database.query() method to get Aggregate query result. We can use alias as well if we need.

//without alias

List<AggregateResult> aggResult - Database.query( 'SELECT Count (Id) FROM Account');

System.debug(aggResult[0].get ('expre'));

//with alias

List<AggregateResult> aggResult  = Database.query ('SELECT Accountld accId, Count (Id) contactCount FROM Contact GROUP RY ACCOUNT’)

System.debug(aggResult[0].get ('accId') + ' ' + aggResult [0].get ('contactCount'));