Why can't I specify both a Primary Key and a Unique Constraint on the same table?

Question

I'm trying to create a table:

CREATE TABLE [MyTable]
(
    [Id] [int] IDENTITY,
    [Column1] [int] NOT NULL,
    [Column2] [int] NOT NULL

    CONSTRAINT [PK_MyTable_Id] PRIMARY KEY ([Id])
    CONSTRAINT [UQ_MyTable_Column1_Column2] UNIQUE ([Column1], [Column2])
)

This script fails with the error:

Both a PRIMARY KEY and UNIQUE constraint have been defined for column 'Column2', table 'MyTable'. Only one is allowed.

Why is this restriction enforced? How can I create a table with these properties?

Answer 1

You missed a comma after the primary key constraint.

CREATE TABLE [MyTable]
(
    [Id] [int] IDENTITY,
    [Column1] [int] NOT NULL,
    [Column2] [int] NOT NULL

    CONSTRAINT [PK_MyTable_Id] PRIMARY KEY ([Id]),
    CONSTRAINT [UQ_MyTable_Column1_Column2] UNIQUE ([Column1], [Column2])
)

Answer 2

CREATE TABLE [MyTable]
(
    [Id] [int] IDENTITY,
    [Column1] [int] NOT NULL,
    [Column2] [int] NOT NULL

    CONSTRAINT [PK_MyTable_Id] PRIMARY KEY ([Id])

)

  ALTER TABLE [MyTable] ADD CONSTRAINT [UQ_MyTable_Column1_Column2] UNIQUE ([Column1], [Column2])