Question

I am converting to an integer primary key and am having trouble seeding the new column data with a count of integer numbers.

Given an existing table:

create table t1 (
  Id uniqueidentifier, 
  NewId int,
  Data nvarchar(100)
)

How would I update existing rows with a count of numbers from 1 to the # of rows in the result set?

So:

|id      |NewId       |Data
-------------------------------
|ABC     |null        |first
|DEF     |null        |second
|GHI     |null        |third

Would become:

|id      |NewId    |Data
----------------------------
|ABC     |1        |first
|DEF     |2        |second
|GHI     |3        |third

This is for a migration to using a hilo primary key with nhibernate, which is needed to reduce database round trips with between my application and database tiers, so IDENTITY is not an option for me.

Answer 1

You could use a windowing function like row_number:

update t
set NewId = sub.rn
from YourTable t
join (
    select
        id
    ,   row_number() over (order by id) as rn
    from YourTable
) sub on sub.id = t.id