output.txt

(1 row(s) affected)
1
Msg 8117, Level 16, State 1, Procedure proc1, Line 6
Operand data type nvarchar(max) is invalid for avg operator.

test.sql

IF  EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[Table_1]') AND type in (N'U'))
DROP TABLE [dbo].[Table_1]
GO

CREATE TABLE [dbo].[Table_1] ([Id] int identity, [Some] int NULL)
GO

IF  EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[proc1]') AND type in (N'P', N'PC'))
DROP PROCEDURE [dbo].[proc1]
GO

CREATE PROCEDURE [dbo].[proc1]
AS
BEGIN
	declare @cnt int
	SELECT @cnt = avg([Some]) from Table_1
	print @cnt
END

GO
insert into Table_1 ([Some]) values (1)
GO

exec proc1 

alter table Table_1 drop column [Some]
go
alter table Table_1 add [Some] nvarchar(max) null
go
exec proc1