I'm sure this is easy but I'm still getting syntax errors when I run it in SQL Server Management Studio v17.4. 

I have table T1 which has serial numbers, and I just need to iterate through and check how many times they appear in T2. I tried like 

```
declare @serial int

select @serial = select serial from T1

while @serial
begin
    select count(*) from T2 where Serial = @serial
end

```

But I get an error:

> 
> Incorrect syntax near the keyword 'select'
> 
> 
> 

How to do it? Thanks.