A field in MS-SQL server batch modification table can be null

--Dangerous operation, remember to backup database 1 declare @ SQL varchar (500) before processing ,@tbname  varchar(100)
 2 begin
 3 
 4 -- create cursor
 5 　　declare cursor_item cursor fast_forward for select [name] from sysobjects where xtype='U' AND id in(select id from syscolumns where name='myColumnName' and colstat=0 )
 6 　　open cursor_ Item; -- Open cursor
 7 while 1 = 1 -- start loop
 8 　　begin
 9 　　　　fetch next from cursor_ Item into @ TBNAME; -- assign to variable
10 　　　　if(@@fetch_ Status! = 0) break; -- exit loop 11 if there is no result
12 -- splicing SQL statements for modifying fields
13 　　　　set @sql = 'alter table '[email protected]+' alter column myColumnName int NULL'
14 
15 -- perform SQL splicing
16 　　　　exec(@sql);
17 
18 　　end
19 　　close cursor_ Item -- close cursor
20 　　deallocate cursor_item
21 
22 end;