SQL Compare rows - mysql

Question

Okay here is the situation:
I the following data in a table.
PAIR_NO NO NO2
3 5678EFGH 1234ABCD
4 1111BBBB 0000AAAA
1 1234ABCD 5678EFGH
2 0000AAAA 1111BBBB
The constraints are if no = no2 in another row skip that row.
So in this sample data the only rows that would be selected should be pair no 3 and 4.
I have tried to merge and inner join with self but I just keep getting all 4 rows back.
I have tried to insert into a table where not exists but again I get 4 rows inserted.
SELECT a.* from PAIRS a
inner join PAIRS b on a.no=b.no2 and a.no2=b.no;
I was thinking maybe selecting distinct number from column 1 and then check those in column 2 but I think that would yield the same four rows.
I may be over thinking this problem and maybe some here can look at this and see where the solution is hiding.
I am currently testing this on MySQL but it should run on SQLServer 2008. I have searched but all the questions didn't seem to match my data set issue.

Answer 1

Taking you at your word, meaning selecting all records where the value of no column does not appear anywhere in no2 column in the same table, try this:
SELECT A.PAIR_NO, A.NO, A.NO2
FROM PAIRS A
LEFT JOIN PAIRS B ON(A.NO = B.NO2)
WHERE B.PAIR_NO IS NULL -- assuming this column is not nullable
Another option is to use NOT EXISTS:
SELECT PAIR_NO, NO, NO2
FROM PAIRS A
WHERE NOT EXISTS(
SELECT 1
FROM PAIRS B
WHERE B.NO2 = A.NO
)
I personally prefer the LEFT JOIN option since it's shorter and more readable.
Both of these statement should work on both MySql and Sql Server.

Answer 2

Okay fellas I want to thank you all for helping, but I think I solved my issue. Took me a second but I believe this is what I am after (SQL Server 2008):
if OBJECT_ID('tempdb..#pairs') is not null drop table #pairs
if OBJECT_ID('tempdb..#pairs_final') is not null drop table #pairs_final
create table #pairs(pair_no int, a_no varchar(17),a_no2 varchar(17))
create table #pairs_final(pair_no int Identity(1,1), a_no varchar(17),a_no2 varchar(17))
insert into #PAIRS values(1,'1234ABCD','5678EFGH');
insert into #PAIRS values(1,'1234ABCD','XXXX9999');
insert into #PAIRS values(2,'0000AAAA','1111BBBB');
insert into #PAIRS values(3,'5678EFGH','1234ABCD');
insert into #PAIRS values(4,'1111BBBB','0000AAAA');
insert into #PAIRS values(1,'XXXX9999','1234ABCD');
insert into #pairs_final
select a.a_no,a.a_no2 from #pairs a
join (
select distinct a_no_p from(
select pair_no,a_no_p,
ROW_NUMBER() over (partition by pair_no order by a_no_p) as RN
from #pairs
unpivot(
a_no_p for clms in (a_no2,a_no)
) as umpvt
) as mypairs
where RN = 1
) as my_pairs on my_pairs.a_no_p=a.a_no
select * from #pairs_final
This will give me the following results:
pair_no a_no a_no2
1 1234ABCD 5678EFGH
2 1234ABCD XXXX9999
3 0000AAAA 1111BBBB
Hope this might help someone else.
Enjoy.

Answer 3

DECLARE #TBL AS TABLE
(
[NO] INT,
[CODE] VARCHAR(50),
[AREA] VARCHAR(50)
)
/* EXAMPLE 1 */
INSERT INTO #TBL([NO],[CODE],[AREA]) VALUES (1,'001','A00')
INSERT INTO #TBL([NO],[CODE],[AREA]) VALUES (2,'001','A00')
INSERT INTO #TBL([NO],[CODE],[AREA]) VALUES (3,'001','B00')
INSERT INTO #TBL([NO],[CODE],[AREA]) VALUES (4,'001','C00')
INSERT INTO #TBL([NO],[CODE],[AREA]) VALUES (5,'001','C00')
INSERT INTO #TBL([NO],[CODE],[AREA]) VALUES (6,'001','A00')
INSERT INTO #TBL([NO],[CODE],[AREA]) VALUES (7,'001','A00')
/* EXAMPLE 2 */
/* ***** USE THIS CODE TO ENTER DATA FROM DIRECT TABLE *****
SELECT
ROW_NUMBER() OVER(ORDER BY [FIELD_DATE]) AS [NO]
,[FIELD_CODE] AS [CODE]
,[FIELD_AREA] AS [AREA]
FROM TABLE_A
WHERE CAST([FIELD_DATE] AS DATE) >= CAST('20200307' AS DATE)
ORDER BY [FIELD_DATE],[FIELD_CODE]
*/
SELECT
A.NO AS ANO
,A.CODE AS ACODE
,A.AREA AS AAREA
,B.NO AS BNO
,B.CODE AS BCODE
,B.AREA AS BAREA
,CASE WHEN A.AREA=B.AREA THEN 'EQUAL' ELSE 'NOT EQUAL' END AS [COMPARE AREA]
FROM #TBL A
LEFT JOIN #TBL B
ON A.NO=B.NO+1