Adding a uniqueidentifier column and adding the default to generate new guid

Question

I have the following SQL command:

ALTER TABLE dbo.UserProfiles
ADD ChatId UniqueIdentifier NOT NULL,
UNIQUE(ChatId),
CONSTRAINT \"ChatId_default\" SET DEFAUL         


        

Answer 1

see this sample:

create table test (mycol UniqueIdentifier NOT NULL default newid(), name varchar(100))
insert into test (name) values ('Roger Medeiros')
select * from test

for add a not null field on a populated table you need this.

alter table test add mycol2 UniqueIdentifier NOT NULL default newid() with values

CREATE UNIQUE NONCLUSTERED INDEX IX_test ON dbo.test
(
mycol
) WITH( STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON,    ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]

Answer 2

Don't use newid() as default, instead use newsequentialid(). newid() creates a lot of fragmentation and that's bad for indexes.

As far as adding the new column to a table with existing data, simply do this:

    ALTER TABLE your_table
    ADD your_column UNIQUEIDENTIFIER DEFAULT newsequentialid() NOT null