Only allow one checked row in a Column in SQL Server Background: 

I've only just begun programming in SQL... barely begun even. But I have been thrown into the deep-end left to find a way and learn to program SQL.

Question:

Is is possible to have a boolean column in a table that only allows one checked row.
So even if a user wanted to update the table with another checked row they wouldn't be able to? Suggestions and Ideas and use layman terms please.

Attempted illustration:

ID        Col_1        Col_2       Boolean_Col
----------------------------------------------
1         Data       More Data         0
2         Data       More Data        -1
3         Data       More Data         0
No

While strictly speaking it can be achieved, it is always a bad idea. In general thinking at restricting properties of sets is a bad road to travel because set property enforcement usually require inspecting the entire set to validate the constraint. In other words enforcing your 'single row check' requires to scan every other row, on every change. This is not only slow, more importantly is the 100% guaranteed recipe for deadlocks.

It would be much better if you post your actual problem rather than ask how to implement the solution you choose.