public class PR_Account
    {
        public string No { get; set; }
        public string Name { get; set; }
        public int AccountType { get; set; }
        public byte Blocked { get; set; }
        public byte DirectPosting { get; set; }
        public int Indentation { get; set; }
        public string Totaling { get; set; }
        public int Type { get; set; }
    }

public class PR_GLEntry
    {
        public int EntryNo { get; set; }
        public string AccountNo { get; set; }
        public decimal Amount { get; set; }
        public string DocumentNo { get; set; }
        public string Description { get; set; }
        public string BalAccountNo { get; set;        }
        public int BalAccountType { get; set; }
        public int SourceType { get; set; }
        public string SourceNo { get; set; }
        public DateTime PostingDate { get; set; }
        public DateTime DocumentDate { get; set; }
    }

SELECT [No]
      ,[Name]
      ,(select sum([Amount])
	    from [dbo].[PR_GLEntries] G
		where G.[AccountNo] = A.No)
  FROM [Pronet2].[dbo].[PR_Accounts] A

   public class AccountSum
    {
        public PR_Account Account { get; set; }
        public decimal Sum { get; set; }

        public static List<AccountSum> GetByDate(PRContext db, DateTime reportDate)
        {
            var res = db.PR_Accounts.GroupJoin(db.PR_GLEntries
                , a => a.No
                , g => g.AccountNo
                , (acc, sumAcc) =>
                new AccountSum { Account = acc, Sum = sumAcc.Sum(ga => ga.Amount) }).ToList();

            return res;
         }
    }

SELECT [a].[No], [a].[AccountType], [a].[Blocked], [a].[DirectPosting], [a].[Indentation], [a].[Name], [a].[Totaling], [a].[Type], [g].[EntryNo], [g].[AccountNo], [g].[Amount], [g].[BalAccountNo], [g].[BalAccountType], [g].[Description], [g].[DocumentDate], [g].[DocumentNo], [g].[PostingDate], [g].[SourceNo], [g].[SourceType]
FROM [PR_Accounts] AS [a]
LEFT JOIN [PR_GLEntries] AS [g] ON [a].[No] = [g].[AccountNo]
ORDER BY [a].[No]

SELECT [a].[No], [a].[AccountType], [a].[Blocked], [a].[DirectPosting], [a].[Indentation], [a].[Name], [a].[Totaling], [a].[Type],
 [g].[EntryNo], [g].[AccountNo], [g].[Amount], [g].[BalAccountNo], [g].[BalAccountType], [g].[Description], [g].[DocumentDate], 
[g].[DocumentNo], [g].[PostingDate], [g].[SourceNo], [g].[SourceType]
FROM [PR_Accounts] AS [a]
LEFT JOIN [PR_GLEntries] AS [g] ON [a].[No] = [g].[AccountNo]
ORDER BY [a].[No]

SELECT [No]
      ,[Name]
      ,(select sum([Amount])
	    from [dbo].[PR_GLEntries] G
		where G.[AccountNo] = A.No)
  FROM [Pronet2].[dbo].[PR_Accounts] A

var accsSum = (from o in db.PR_GLEntries
                           where o.PostingDate <= reportDate
                           group o by o.AccountNo into os
                           select new AccountSumShort { AccountNo = os.Key, Sum = os.Sum(o => o.Amount) });

exec sp_executesql N'SELECT TOP(1) [o].[AccountNo], SUM([o].[Amount]) AS [Sum]
FROM [PR_GLEntries] AS [o]
WHERE [o].[PostingDate] <= @__reportDate_0
GROUP BY [o].[AccountNo]
HAVING [o].[AccountNo] = @__acc_No_1',N'@__reportDate_0 datetime2(7),@__acc_No_1 nvarchar(4000)',@__reportDate_0='2018-07-20 00:00:00',@__acc_No_1=N'11000110'

var accsSum = (from o in db.PR_GLEntries
                           where o.PostingDate <= reportDate
                           group o by o.AccountNo into os
                           select new AccountSumShort { AccountNo = os.Key, Sum = os.Sum(o => (double)o.Amount) });