sql-to fetch reciprocal data - sql

Question

I have a table in Oracle db, which contains data like this, a+b, b+a, c+d, d+c.
My question is, when a+b = b+a, how to fetch distinct records.
PK CODE
1000 87DIA4+BAJI204
1001 87DIA4+BIJI939
1002 87DIA4+C3IDI02
1003 87DIA4+C3IZI419
1004 BAJI204+87DIA4
1005 BIJI939+87DIA4
1006 C3IDI02+87DIA4
1007 C3IZI419+87DIA4

Answer 1

Write a sub-query which splits out the two elements from the CODE column. Then use a self-join to find the reciprocal pairs:
SQL> with cte as ( select pk
2 , substr(code, 1, instr(code, '+')-1) as str1
3 , substr(code, instr(code, '+')+1) as str2
4 from your_table)
5 select a.pk as a_pk
6 , b.pk as b_pk
7 , a.str1
8 , a.str2
9 from cte a
10 join cte b
11 on a.str1 = b.str2
12 and a.str2 = b.str1
13 where a.pk < b.pk
14 order by a_pk;
A_PK B_PK STR1 STR2
---------- ---------- ------------ ------------
1000 1004 87DIA4 BAJI204
1001 1005 87DIA4 BIJI939
1002 1006 87DIA4 C3IDI02
1003 1007 87DIA4 C3IZI419
4 rows selected.
SQL>
The WHERE clause ensures the result set contains only one instance of each reciprocal pair.

Answer 2

If I understand your question, you may need something like this:
with yourTable(PK, CODE) as (
select '1000', '87DIA4+BAJI204' from dual union all
select '1001', '87DIA4+BIJI939' from dual union all
select '1002', '87DIA4+C3IDI02' from dual union all
select '1003', '87DIA4+C3IZI419' from dual union all
select '1004', 'BAJI204+87DIA4' from dual union all
select '1005', 'BIJI939+87DIA4' from dual union all
select '1006', 'C3IDI02+87DIA4' from dual union all
select '1007', 'C3IZI419+87DIA4' from dual
)
select least( substr(code, 1, instr(code, '+') -1), substr(code, instr(code, '+') +1)) as A,
greatest( substr(code, 1, instr(code, '+') -1), substr(code, instr(code, '+') +1)) as B
from yourTable
group by least( substr(code, 1, instr(code, '+') -1), substr(code, instr(code, '+') +1)),
greatest( substr(code, 1, instr(code, '+') -1), substr(code, instr(code, '+') +1))
that gives:
A B
--------------- ---------------
87DIA4 BAJI204
87DIA4 BIJI939
87DIA4 C3IDI02
87DIA4 C3IZI419
The idea is to separate the values in each row and, for each row, evaluate the "smallest" and the "greatest" value. This way, you can use these results to group and get only one row A+B if you have A+B and B+A.

Answer 3

As Aleksej and APC both pointed out, you need to split the code into components. And I am pleased to see they both offered the "right" solution (rather than the "lazy" solution) - to split code, use standard string functions substr() and instr(), not regular expressions.
The solution below also splits the code, in the same way. I use that for a GROUP BY clause, to group together the rows you consider "duplicates". Then from each group I just pick the one with the lowest PK value. NOTE: your problem statement is incomplete, you didn't state WHICH row should be kept from each pair. (Or, more generally, what to do with them... if the requirement is different, the solution below can be adapted.)
In each group I select MIN(PK) - that is self-explanatory. Then, to pick up the CODE value that belongs to that PK, I use the FIRST function; see the documentation if you are not familiar with it. (Some developers aren't.)
This solution reads the base data just once, and there are no joins.
with
test_data ( pk, code ) as (
select 1000, '87DIA4+BAJI204' from dual
union all select 1001, '87DIA4+BIJI939' from dual
union all select 1002, '87DIA4+C3IDI02' from dual
union all select 1003, '87DIA4+C3IZI419' from dual
union all select 1004, 'BAJI204+87DIA4' from dual
union all select 1005, 'BIJI939+87DIA4' from dual
union all select 1006, 'C3IDI02+87DIA4' from dual
union all select 1007, 'C3IZI419+87DIA4' from dual
)
-- End of test data (not part of the solution!) SQL query begins BELOW THIS LINE.
select min(pk) as pk, min(code) keep (dense_rank first order by pk) as code
from test_data
group by least(substr(code, 1, instr(code, '+')-1), substr(code, instr(code, '+')+1)),
greatest(substr(code, 1, instr(code, '+')-1), substr(code, instr(code, '+')+1))
;
PK CODE
---- ---------------
1000 87DIA4+BAJI204
1001 87DIA4+BIJI939
1002 87DIA4+C3IDI02
1003 87DIA4+C3IZI419