SELECT COUNT(*) AS [Records], SUM(t.Amount) AS [Total]
FROM   dbo.t1 AS t
WHERE  t.Id > 0
       AND t.Id < 101;

Arithmetic overflow error converting expression to data type int.

SELECT COUNT_BIG(*) AS [Records], SUM(t.Amount) AS [Total]
FROM   dbo.t1 AS t
WHERE  t.Id > 0
       AND t.Id < 101;

SELECT COUNT(*) AS [Records], SUM(CONVERT(BIGINT, t.Amount)) AS [Total]
FROM   dbo.t1 AS t
WHERE  t.Id > 0
       AND t.Id < 101;

SELECT COUNT(*) AS [Records], SUM(CAST(t.Amount AS BIGINT)) AS [Total]
FROM   dbo.t1 AS t
WHERE  t.Id > 0
       AND t.Id < 101;