Compare 2 or more column values in arbitrary order - sql

Question

I need a quick way to compare 2 or more values from different tables where the orders are arbitrarily stored in sql server. The data comes from a 3rd party who will not change.
Example data below shows the same item described in two ways. the remaining columns contain other data that i am joining.
table1
i j other columns...
1 2 ...
table2
i j other columns
2 1 ...
1 2 ...
right now for 2, i do a union query to cover both directions (i=i, j=j / i=j, j=i) . but if you expand to 3, that is 9 possible orders.
SELECT * FROM Table1 INNER JOIN Table2 ON Table1.i = Table2.i AND Table1.j = Table2.j
UNION
SELECT * FROM Table1 INNER JOIN Table2 ON Table1.i = Table2.j AND Table1.j = Table2.i
is there a way to order data returned from the first two columns before doing the comparison so i don't have to create all the unions?

Answer 1

Edit: New xml approach
I wonder how this approach performs:
select *, cast( '<c>' + cast(i as varchar) + '</c>' +
'<c>' + cast(j as varchar) + '</c>' +
'<c>' + cast(k as varchar) + '</c>'
as xml).query('for $a in /c order by $a return concat($a, "/")').value('.', 'varchar(100)')
from #Table1 o
This can be wrapped in a function and referenced in a persisted column... which should scale very well for you:
create table dbo.Table1 (pk int identity(1,1) primary key, i int, j int, k int);
insert into dbo.Table1
values(1, 2, 3), (3, 1, 2), (4, 5, 6), (9,9,9);
go
create function dbo.fn_GenerateCompare(#i int, #j int, #k int)
returns varchar(100)
with schemabinding
as
begin
return
(
select cast('<c>' + cast(#i as varchar) + '</c>' +
'<c>' + cast(#j as varchar) + '</c>' +
'<c>' + cast(#k as varchar) + '</c>'
as xml).query('for $a in /c order by $a return concat($a, "/")').value('.', 'varchar(100)')
);
end
alter table dbo.Table1
add Compare as dbo.fn_GenerateCompare(i, j, k) persisted;
select * from dbo.Table1
Returns:
pk i j k Compare
-- - - - -------
1 1 2 3 1/2/3
2 3 1 2 1/2/3
3 4 5 6 4/5/6
4 9 9 9 9/9/9
Your query should now be really simple. Slap an index on the new Compare column and it should fly.
Original Post:
I like the sorted list idea proposed by Thorsten. Heres a rough idea of how it might be done. Performance would be greatly improved by persisting this compare column on the table (trigger or persisted computed column?)
declare #Table1 table (pk int identity(1,1) primary key, i int, j int, k int)
declare #Table2 table (pk int identity(1,1) primary key, i int, j int, k int)
insert into #Table1
values(1, 2, 3), (3, 1, 2), (4, 5, 6), (9,9,9)
insert into #Table2
values (2, 1, 3), (6, 4, 5)
--since the order is unimportant, concatenate the columns into a sorted array
--note how 1,2,3 and 3,1,2 both result in the same compare value:
select *
from #Table1 o
cross
apply ( select cast(value as varchar) + '/'
from #Table1
unpivot (value for c in (i,j,k)) as u
where pk = o.pk
order
by value
for xml path('')
)d(compare)
--now, bring in the 2nd table
select [src] = 1, pk, compare
from #Table1 o
cross
apply ( select cast(value as varchar) + '/'
from #Table1
unpivot (value for c in (i,j,k)) as u
where pk = o.pk
order
by value
for xml path('')
)d(compare)
union all
select [src] = 2, pk, compare
from #Table2 o
cross
apply ( select cast(value as varchar) + '/'
from #Table2
unpivot (value for c in (i,j,k)) as u
where pk = o.pk
order
by value
for xml path('')
)d(compare)
--now just group them to find the matching rows
select min(src), min(pk), compare
from (
select [src] = 1, pk, compare
from #Table1 o
cross
apply ( select cast(value as varchar) + '/'
from #Table1
unpivot (value for c in (i,j,k)) as u
where pk = o.pk
order
by value
for xml path('')
)d(compare)
union all
select [src] = 2, pk, compare
from #Table2 o
cross
apply ( select cast(value as varchar) + '/'
from #Table2
unpivot (value for c in (i,j,k)) as u
where pk = o.pk
order
by value
for xml path('')
)d(compare)
)grouped
group
by compare
having count(*) > 1;