TSQL Comparing two Sets - sql

Question

When two sets are given
s1 ={ a,b,c,d} s2={b,c,d,a}
(i.e)
TableA
Item
a
b
c
d
TableB
Item
b
c
d
a
How to write Sql query to display "Elements in tableA and tableB are equal". [Without using SP or UDF]
Output
Elements in TableA and TableB contains identical sets

Answer 1

Use:
SELECT CASE
WHEN COUNT(*) = (SELECT COUNT(*) FROM a)
AND COUNT(*) = (SELECT COUNT(*) FROM b) THEN 'Elements in TableA and TableB contains identical sets'
ELSE 'TableA and TableB do NOT contain identical sets'
END
FROM (SELECT a.col
FROM a
INTERSECT
SELECT b.col
FROM b) x
Test with:
WITH a AS (
SELECT 'a' AS col
UNION ALL
SELECT 'b'
UNION ALL
SELECT 'c'
UNION ALL
SELECT 'd'),
b AS (
SELECT 'b' AS col
UNION ALL
SELECT 'c'
UNION ALL
SELECT 'd'
UNION ALL
SELECT 'a')
SELECT CASE
WHEN COUNT(*) = (SELECT COUNT(*) FROM a)
AND COUNT(*) = (SELECT COUNT(*) FROM b) THEN 'yes'
ELSE 'no'
END
FROM (SELECT a.col
FROM a
INTERSECT
SELECT b.col
FROM b) x

Answer 2

Something like this, using FULL JOIN:
SELECT
CASE
WHEN EXISTS (
SELECT * FROM s1 FULL JOIN s2 ON s1.Item = s2.Item
WHERE s1.Item IS NULL OR s2.Item IS NULL
)
THEN 'Elements in tableA and tableB are not equal'
ELSE 'Elements in tableA and tableB are equal'
END
This has the virtue of short-circuiting on the first non-match, unlike other solutions that require 2 full scans of each table (once for the COUNT(*), once for the JOIN/INTERSECT).
Estimated cost is significantly less than other solutions.

Answer 3

Watch out, I'm gonna use a Cross Join.
Declare #t1 table(val varchar(20))
Declare #t2 table(val varchar(20))
insert into #t1 values ('a')
insert into #t1 values ('b')
insert into #t1 values ('c')
insert into #t1 values ('d')
insert into #t2 values ('c')
insert into #t2 values ('d')
insert into #t2 values ('b')
insert into #t2 values ('a')
select
case when
count(1) =
(((Select count(1) from #t1)
+ (Select count(1) from #t2)) / 2.0)
then 1 else 0 end as SetsMatch from
#t1 t1 cross join #t2 t2
where t1.val = t2.val

Answer 4

My monstrocity:
;with SetA as
(select 'a' c union
select 'b' union
select 'c')
, SetB as
(select 'b' c union
select 'c' union
select 'a' union
select 'd'
)
select case (select count(*) from (
select * from SetA except select * from SetB
union
select * from SetB except select * from SetA
)t)
when 0 then 'Equal' else 'NotEqual' end 'Equality'

Answer 5

Could do it with EXCEPT and a case
select
case
when count (1)=0
then 'Elements in TableA and TableB contains identical sets'
else 'Nope' end from (
select item from s1
EXCEPT
select item from s2
) b

Answer 6

Since this thread was very helpful to me, I thought I'd share my solution.
I had a similar problem, perhaps more generally applicable than this specific single-set comparison. I was trying to find the id of an element that had a set of multi-element child elements that matched a query set of multi-element items.
The relevant schema information is:
table events, pk id
table solutions, pk id, fk event_id -> events
table solution_sources, fk solutionid -> solutions
columns unitsourceid, alpha
Query: find the solution for event with id 110 that has the set of solution_sources that match the set of (unitsourceid, alpha) in ss_tmp. (This can also be done without the tmp table, I believe.)
Solution:
with solutionids as (
select y.solutionid from (
select ss.solutionid, count(ss.solutionid) x
from solutions s, solution_sources ss
where s.event_id = 110 and ss.solutionid = s.id
group by ss.solutionid
) y where y.x = ( select count(*) from ss_tmp )
)
select solutionids.solutionid from solutionids where
(
select case
when count(*) = ( select count(*) from ss_tmp ) then true
else false
end
from
( SELECT unitsourceid, alpha FROM solution_sources
where solutionid = solutionids.solutionid
INTERSECT
SELECT unitsourceid, alpha FROM ss_tmp ) x
)
Tested against a test query of 4 items and a test db that had a matching solution (same number of child elements, each that matched), several completely non-matching solutions, and 1 solution that had 3 matching child elements, 1 solution that had all 4 matching child elements, plus an additional child, and 1 solution that had 4 child elements of which 3 of the 4 matched the query. Only the id of the true match was returned.
thanks a lot
-Linus

Answer 7

Use EXCEPT statement
When using the EXCEPT statement to test if two sets contain the same rows, you will need to do the EXCEPT in both directions (A EXCEPT B and B EXCEPT A). If either comparison returns any records, then the sets are different. If no records are returned by either, they are the same.
The nice thing about this is that you can do this comparison with any number of specific columns and NULL values are handled implicitly without having to jump through hoops to compare them.
A good use case for this is verifying that saving a set of records happened correctly, especially when affecting an existing set.
SELECT IsMatching = (1 ^ convert(bit, count(*)))
FROM (
SELECT Mismatched = 1 -- Can be any column name
FROM (
SELECT Item -- Can have additional columns
FROM TableA
EXCEPT
SELECT Item -- Can have additional columns
FROM TableB
) as A
UNION
SELECT Mismatched = 1 -- Can be any column name
FROM (
SELECT Item -- Can have additional columns
FROM TableB
EXCEPT
SELECT Item -- Can have additional columns
FROM TableA
) as A
) as A