Merge with primary key violation - sql

Question

I have a file based import thingy where the users can post files to be imported in the database. New records are inserted and records with an already existing Id are updated.
After posting a file with
ID NAME
5 Silly
they can correct this by posting a new file with
ID NAME
5 Sally
I have a bulk insert (C# windows service) of the file into a bulk table (Sql Server Azure v12). The files can contain millions of rows so I'd like to avoid iterating through rows. After the bulk insert i have a SP that does a merge update / insert and updates already existing rows and inserts new ones.
The problem I've come across is when the users post a new record and a correction of the same record in the same file. I get a PRIMARY KEY VIOLATION on the target table.
Is there a nice way to solve this?
Here's an example:
--drop table #bulk
--drop table #target
create table #bulk(
id int,
name varchar(10)
)
insert into #bulk values (1,'John')
insert into #bulk values (2,'Sally')
insert into #bulk values (3,'Paul')
insert into #bulk values (4,'Gretchen')
insert into #bulk values (5,'Penny')
insert into #bulk values (5,'Peggy')
create table #target(
id int not null,
name varchar(10),
primary key (id))
merge #target as target
using(select id, name from #bulk) as bulktable
on target.id = bulktable.id
when matched then update
set target.name = bulktable.name
when not matched then
insert(id, name) values (bulktable.id, bulktable.name);

Answer 1

This will handle the latest value for name.
You need a new create script for #bulk
CREATE TABLE #bulk
(
row_id int identity(1,1),
id int,
name varchar(10)
)
This is the script you can use with the new bulk table:
;WITH CTE as
(
SELECT
id, name,
row_number() over (partition by id order by row_id desc) rn
FROM #bulk
), CTE2 as
(
SELECT id, name
FROM CTE
WHERE rn = 1
)
MERGE #target as target
USING CTE2 as bulktable
on target.id = bulktable.id
WHEN matched and
not exists(SELECT target.name except SELECT bulktable.name)
-- this will handle null values. Otherwise it could simply have been:
-- matched and target.name <> bulktable.name
THEN update
SET target.name = bulktable.name
WHEN not matched THEN
INSERT(id, name) VALUES (bulktable.id, bulktable.name);