Question

SequenceId is an auto-incrementing identity column, but isn’t the primary key.

What I want to happen is that when a row is updated, SequenceId is set to the next available value, e.g.:

_____________________
| SequenceId | Name |
| 1          | John |
| 2          | Jane |
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Update John to Jack. SequenceId is set to the next available identity value.

_____________________
| SequenceId | Name |
| 3          | Jack |
| 2          | Jane |
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Is this possible with SQL Server? If not, what would be an alternative?

Answer 1

I don’t think you can, at least not easily or cleanly. Why not use a ROWVERSION column? ROWVERSION columns are updated every time the row is updated to a new unique incrementing value in the database. You can create a computed column that converts it to a bigint if you want to index it. The downside is that timestamps are database-wide so you could get skipped numbers if you have multiple tables that use them.

FIDDLE

create table TestRowVersion (
    Id int primary key,
    Name varchar(20),
    BinaryRowVersion ROWVERSION,
    IntegerRowVersion as convert(BIGINT, BinaryRowVersion)
)   

create index IDX_TestRowVersion on TestRowVersion (IntegerRowVersion)

insert into TestRowVersion (Id, Name) values (1, 'Alvin')
insert into TestRowVersion (Id, Name) values (2, 'Betsy')
insert into TestRowVersion (Id, Name) values (3, 'Charles')
select * From TestRowVersion
update TestRowVersion set Name = 'Frank' where Id = 2
select * From TestRowVersion

[EDIT] – updated to use RowVersion since Timestamp is deprecated