sql server - Change type of a column with numbers from varchar to int

Question

We have two columns in a database which is currently of type varchar(16). Thing is, it contains numbers and always will contain numbers. We therefore want to change its type to integer. But the problem is that it of course already contains data.

Is there any way we can change the type of that column from varchar to int, and not lose all those numbers that are already in there? Hopefully some sort of sql we can just run, without having to create temporary columns and create a C# program or something to do the conversion and so forth... I imagine it could be pretty easy if SQL Server have some function for converting strings to numbers, but I am very unstable on SQL. Pretty much only work with C# and access the database through LINQ to SQL.

Note: Yes, making the column a varchar in the first place was not a very good idea, but that is unfortunately the way they did it.

Answer 1

The only reliable way to do this will be using a temporary table, but it will not be much SQL:

select * into #tmp from bad_table
truncate table bad_table
alter bad_table alter column silly_column int
insert bad_table
select cast(silly_column as int), other_columns
from #tmp
drop table #tmp