Oracle SQL merge half empty query lines - sql

Question

I have an Oracle12 and a table
Debit
Credit
a1
b1
c1
a1
c2
a1
b2
a2
a2
b3
a2
c2
no rows with a%+a% and b%+b%
I want to select 4 columns: Debit+Credit where exists a% and not b% in any column
and Debit+Credit where exists a% and b% in any column. The first column pair must correspond the second by a% value.
Something like
with t as (
select 'a1' Debit, 'b1' Credit from dual
union all select 'c1', 'a1' from dual
union all select 'c2', 'a1' from dual
union all select 'b2', 'a2' from dual
union all select 'a2', 'b3' from dual
union all select 'a2', 'c2' from dual)
select Debit, Credit, null DebitB, null CreditB
from t
where (Debit like 'a%' or Credit like 'a%')
and (Debit not like 'b%' and Credit not like 'b%')
union all
select null, null, Debit, Credit
from t
where (Debit like 'a%' or Credit like 'a%')
and (Debit like 'b%' or Credit like 'b%')
but merge (exclude empty cells if possible) these 6 rows into 4 "grouped" by a%. At first all merged rows with a1, then all merged rows with a2 and so on. Any order within group, nulls last. The result must be
Debit
Credit
DebitB
CreditB
c1
a1
a1
b1
c2
a1
a2
c2
b2
a2
a2
b3

Answer 1

You can number the rows and use a FULL OUTER JOIN matching on the a values and the row number:
SELECT t1.Debit,
t1.Credit,
t2.debit AS DebitB,
t2.credit AS CreditB
FROM (
SELECT t.*,
ROW_NUMBER() OVER (
PARTITION BY CASE WHEN debit LIKE 'a%' THEN debit ELSE credit END
ORDER BY CASE WHEN debit LIKE 'a%' THEN credit ELSE debit END
) AS rn
FROM t
WHERE debit LIKE 'a%' AND credit NOT LIKE 'b%'
OR debit NOT LIKE 'b%' AND credit LIKE 'a%'
) t1
FULL OUTER JOIN (
SELECT t.*,
ROW_NUMBER() OVER (
PARTITION BY CASE WHEN debit LIKE 'a%' THEN debit ELSE credit END
ORDER BY CASE WHEN debit LIKE 'a%' THEN credit ELSE debit END
) AS rn
FROM t
WHERE debit LIKE 'a%' AND credit LIKE 'b%'
OR debit LIKE 'b%' AND credit LIKE 'a%'
) t2
ON CASE WHEN t1.debit LIKE 'a%' THEN t1.debit ELSE t1.credit END
= CASE WHEN t2.debit LIKE 'a%' THEN t2.debit ELSE t2.credit END
AND t1.rn = t2.rn
Which, for the sample data:
CREATE TABLE t (debit, credit) as
select 'a1', 'b1' from dual union all
select 'c1', 'a1' from dual union all
select 'c2', 'a1' from dual union all
select 'b2', 'a2' from dual union all
select 'a2', 'b3' from dual union all
select 'a2', 'c2' from dual;
Outputs:
DEBIT
CREDIT
DEBITB
CREDITB
c1
a1
a1
b1
a2
c2
b2
a2
null
null
a2
b3
c2
a1
null
null
fiddle