Needing system defined function to select updated or unmatched new records from two tables - sql

Question

I am having a live data table in which the old values are placed,in a new table i am moving data from that live table to this one how to find updated or new records that are inserted or updated in new table with out using except,checksum(binary_checksum) and join ,i am looking for a solution using System Defined Function.

Answer 1

The requirement is interesting as the best solutions are to use EXCEPT or a FULL JOIN. What you are trying to do is what is referred to as an left anti semi join. Here's a good article about the topic.
Note this sample data and the solutions (note that my solution that does not use EXCEPT or a join is the last solution):
-- sample data
if object_id('tempdb.dbo.orig') is not null drop table dbo.orig;
if object_id('tempdb.dbo.new') is not null drop table dbo.new;
create table dbo.orig (someid int, col1 int, constraint uq_cl_orig unique (someid, col1));
create table dbo.new (someid int, col1 int, constraint uq_cl_new unique (someid, col1));
insert dbo.orig values (1,100),(2,110),(3,120),(4,2000)
insert dbo.new values (1,100),(2,110),(3,122),(5,999);
Here's the EXCEPT version
select someid
from
(
select * from dbo.new except
select * from dbo.orig
) n
union -- union "distict"
select someid
from
(
select * from dbo.orig except
select * from dbo.new
) o;
Here's a FULL JOIN Solution which will also tell you if the record was removed, changed or added:
select
someid = isnull(n.someid, o.someid),
[status] =
case
when count(isnull(n.someid, o.someid)) > 1 then 'changed'
when max(n.col1) is null then 'removed' else 'added'
end
from dbo.new n
full join dbo.orig o
on n.col1=o.col1 and n.someid = o.someid
where n.col1 is null or o.col1 is null
group by isnull(n.someid, o.someid);
But, because those efficient solutions are not an option - you will need to go with a NOT IN or NOT EXISTS subquery.... And because it has to be a function, I am encapsulating the logic into a function.
create function dbo.newOrChangedOrRemoved()
returns table as return
-- get the new records
select someid, [status] = 'new'
from dbo.new n
where n.someid not in (select someid from dbo.orig)
union all
-- get the removed records
select someid, 'removed'
from dbo.orig o
where o.someid not in (select someid from dbo.new)
union all
-- get the changed records
select someid, 'changed'
from dbo.orig o
where exists
(
select *
from dbo.new n
where o.someid = n.someid and o.col1 <> n.col1
);
Results:
someid status
----------- -------
5 new
4 removed
3 changed