Obtaining one description from multiple domain tables with Oracle - sql

Question

How can I merge descriptions obtained from three domain tables into a single description column?
There is a transaction table that has transaction ID's and three domain tables that between them have the descriptions for the transaction IDs - something like this:
Transaction Table: TANS_TBL with columns like TRANS_ID, TRANS_START_TM, TRANS_END_TM, TRANS_RESULT_CD
Domain Table 1: DMN_TANS_DESC_TBL1 with columns like TRANS_ID, DMN1_SHORT_DESC, DMN1_LONG_DESC
Domain Table 2: DMN_TANS_DESC_TBL2 with columns like TRANS_ID, DMN2_SHORT_DESC, DMN2_LONG_DESC
Domain Table 3: DMN_TANS_DESC_TBL3 with columns like TRANS_ID, DMN3_SHORT_DESC, DMN3_LONG_DESC
The rows for the TRANS_ID and short descriptions are not unique
in each table. A TRANS_ID may have multiple rows in a Domain Table.
Only the Short Description is needed; only one row for a
TRANS_ID is wanted.
The column names for descriptions are
different in each domain table.
Any given TRANS_ID will appear in only one domain table (I believe other things in the application will break if that is not true, but I don't see anything to enforce that)
Data needs to be extracted with the column headers like this:
TRANS_ID, TRANS_SHORT_DESC, TRANS_START_TM, TRANS_END_TM
No table modifications or additions are permitted.
Using this, the descriptions can be obtained:
select trns.TRANS_ID, dmn1.DMN1_SHORT_DESC, dmn2.DMN2_SHORT_DESC, dmn3.DMN3_SHORT_DESC
from TRANS_TBL trns
left join DMN_TANS_DESC_TBL1 dmn1 ON dmn1.TRANS_ID=trns.TRANS_ID
left join DMN_TANS_DESC_TBL2 dmn2 ON dmn2.TRANS_ID=trns.TRANS_ID
left join DMN_TANS_DESC_TBL3 dmn3 ON dmn3.TRANS_ID=trns.TRANS_ID;
`
However that has two problems:
Duplicate rows for each domain table description row, and
There are three description columns, two out of three NULL, for each row
One description row from one domain table can be obtained with this:
select TRANS_ID, TRANS_DESC
from ( select dmn1.TRANS_ID, dmn1.DMN1_SHORT_DESC as "TRANS_DESC", row_number()
over( partision by dmn1.TRANS_ID ORDER by dmn1.TRANS_ID) as row_num
from DM_TANS_DESC_TBL1 dmn1
)
where row_num=1;
But I haven't found a way to bring those descriptions from the 3 domain tables into a single transaction ID description column.

Answer 1

You can simply use COALESCE or nested NVL or a DECODE or a CASE statement to combine the columns into one. Something like:
SELECT trans_id,
trans_desc
FROM (SELECT trans_id,
trans_desc,
ROW_NUMBER() OVER (PARTITION BY trans_id ORDER BY DECODE(trans_desc,NULL,2,1) ASC, trans_id DESC) seq
FROM (SELECT trans_tbl.trans_id,
COALESCE(dmn1.dmn1_short_desc,dmn2.dmn2_short_desc,dmn3.dmn3_short_desc) trans_desc
FROM trans_tbl
left join DMN_TANS_DESC_TBL1 dmn1 ON dmn1.TRANS_ID=trns.TRANS_ID
left join DMN_TANS_DESC_TBL2 dmn2 ON dmn2.TRANS_ID=trns.TRANS_ID
left join DMN_TANS_DESC_TBL3 dmn3 ON dmn3.TRANS_ID=trns.TRANS_ID))
WHERE seq = 1
The DECODE in the ROW_NUMBER logic is in order to prefer non-null values over null values.

Answer 2

With your sample data something like here:
WITH
tbl (TRANS_ID, TRANS_START_TM, TRANS_END_TM) AS
(
Select 1, '09:00:00' , '09:01:00' From Dual Union All
Select 2, '09:12:00' , '09:15:00' From Dual Union All
Select 3, '09:16:00' , '09:17:00' From Dual Union All
Select 4, '09:21:00' , '09:22:00' From Dual Union All
Select 5, '09:23:00' , '09:27:00' From Dual
),
desc_tbl_1 (TRANS_ID, DMN1_SHORT_DESC) AS
(
Select 1, 'D1 T1 - some desc' From Dual Union All
Select 1, 'D1 T1 - some desc' From Dual
),
desc_tbl_2 (TRANS_ID, DMN2_SHORT_DESC) AS
(
Select 2, 'D2 T2 - some desc' From Dual Union All
Select 2, 'D2 T2 - some desc' From Dual Union All
Select 3, 'D2 T3 - some desc' From Dual
),
desc_tbl_3 (TRANS_ID, DMN3_SHORT_DESC) AS
(
Select 4, 'D3 T4 - some desc' From Dual Union All
Select 5, 'D3 T5 - some desc ' From Dual
),
... you could create a CTE descriptions to colect them in one column
descriptions (TRANS_ID, TRANS_SHORT_DESC, RN) AS
(
Select TRANS_ID, DMN1_SHORT_DESC, ROW_NUMBER() OVER(Partition By TRANS_ID Order By 1) From desc_tbl_1 Union All
Select TRANS_ID, DMN2_SHORT_DESC, ROW_NUMBER() OVER(Partition By TRANS_ID Order By 1) From desc_tbl_2 Union All
Select TRANS_ID, DMN3_SHORT_DESC, ROW_NUMBER() OVER(Partition By TRANS_ID Order By 1) From desc_tbl_3
)
Main SQL
Select t.TRANS_ID, d.TRANS_SHORT_DESC, t.TRANS_START_TM, t.TRANS_END_TM
From tbl t
Inner Join descriptions d ON(d.TRANS_ID = t.TRANS_ID And d.RN = 1)
Result:
TRANS_ID
TRANS_SHORT_DESC
TRANS_START_TM
TRANS_END_TM
1
D1 T1 - some desc
09:00:00
09:01:00
2
D2 T2 - some desc
09:12:00
09:15:00
3
D2 T3 - some desc
09:16:00
09:17:00
4
D3 T4 - some desc
09:21:00
09:22:00
5
D3 T5 - some desc
09:23:00
09:27:00
NOTE - If there is a possibility that some ID has no description from 3 domains then use Left Join and handle null value.