use tempdb
go
if object_id('dbo.test1') is not null drop table dbo.test1
go
create table dbo.test1(f1 varchar(50))
go
create index idx1 on dbo.test1(f1)
go
insert dbo.test1 values('AAA')
go
select COLUMNPROPERTY(OBJECT_ID('dbo.test1'), 'f1', 'Precision') as 'BEFORE'
go
alter table dbo.test1 alter column f1 varchar(100)
go
select COLUMNPROPERTY(OBJECT_ID('dbo.test1'), 'f1', 'Precision') as 'AFTER'