如何基于另一列定义计算的约束列

Question

I would like adding a default constrain to a column based on another column using Scalar-valued function

These is an example:

CREATE TABLE [MyTable] 
(
    [Id] [int] NOT NULL
    [ScrambledId] [int] NOT NULL
)

ALTER TABLE [MyTable] ADD DEFAULT (dbo.MakeItScrambled([Id])) FOR [ScrambledId]

CREATE function [dbo].MakeItScrambled(@Value int)
BEGIN
    --Some logic
    retrun @ScrambledValue
END

I need the column [ScrambledId] to be Scrambled based on column [Id]

It seems that the Column Names are not permitted:

The name "Id" is not permitted in this context. Valid expressions are constants, constant expressions, and (in some contexts) variables. Column names are not permitted.

Any suggestions?

Answer 1

You have not added a calculated column you have created a normal column and tried to add a default to it. You cannot reference another column in a default constraint.

Edit: This will raise error:

Computed column 'ScrambledId' cannot be persisted because the column is non-deterministic

If you want a calculated column then in the table definition use... [ScrambledId] AS dbo.MakeItScrambled([Id]) PERSISTED - I would suggest using persisted where you are calcuting based on a scalar function.

Alternatively you could add an update/insert trigger to set the value of [ScrambledId] when you insert or update [Id].