Alter table column for primary key and identity

Question

I have table created and want to alter that table. I want to add a primary key and identity(1,1).

I can apply primary key but applying identity gives error. Is anything missing?

ALTER TABLE MyTable ADD PRIMARY KEY (Id)

How can I add identity as well with primary key?

Solution

You cannot alter the definition of an existing column in the database, to add the IDENTITY property (nor to remove it). You have to create a new column with the IDENTITY property:

ALTER TABLE MyTable ADD NewID int IDENTITY(1,1) not null

Unfortunately, you're not then able to assign the old ID values to this new column. If you want to assign the ID values, and then let IDENTITY take over, you'd be better off creating a new table with the structure you want, then importing data from the old table (you can use IDENTITY_INSERT to assign values to the IDENTITY column).

You would then drop the old table and rename the new table, if required.

Comments

[k-s]

Yes, thanks for it. I was trying to add identity to my existence column.

[Martin Smith]

You can do this as a metadata only change

[Beytan Kurt]

if Primary Key is also wanted, ALTER TABLE LookupStates ADD Id int IDENTITY(1,1) PRIMARY KEY not null

[chris dorn]

Isn't identity the definition of PK in MSSQL?

[Damien_The_Unbeliever]

@chrisdorn - no, don't confuse separate concepts. A primary key is one or more columns by which each row may be uniquely identified. identity is a means to apply a unique value per row in a single column. One may be used to create the other but they are not the same thing. Generally referred to as a surrogate, and if you don't also have a natural key then you're not modelling data but random assortments of facts.

[Build Succeeded]

Not directly answering the question.