[Solved] SQL Server constraint [closed]

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As I wrote in my comment, I would not set the existing value to null. Instead, a computed column seems like a better option to me.
Also, varchar(1) is the second worst data type you can choose (nvarchar(1) is even worst). First, if you know you only ever going to have a fixed length string, use char or nchar. Second, if it’s only to specify y or n, You better simply use bit, what only holds values of 0 or 1.

CREATE TABLE Example
(
    [status] bit not null, -- 0 for `n`, 1 for `y`
    [originalPath] varchar(70) not null, -- keeps the original value. Think write only.
    [path] as (case when status = 1 then 
                   null 
               else 
                   originalPath 
               end) -- computed column to use in select statements. This is read only.
)

solved SQL Server constraint [closed]