Join by concatenated field (in CSV format) - sql

Question

UPDATE: I am fully aware that this is a poor RDBMS practice, but the question is not asking whether it is and how I can re-train the DBAs who created this architecture. The question is how I can work around the situation that I have on hands. I appreciate the help of the community and must admit that this is an interesting problem indeed.
In SQL Server 2017, I have a lookup table containing codes and a transactions table with CSV-formated codes:
CREATE TABLE #t(cd VARCHAR(100))
CREATE TABLE #cd (id INT, cd VARCHAR (1000))
INSERT INTO #t SELECT 'c1'
INSERT INTO #t SELECT 'c1,c2'
INSERT INTO #t SELECT 'c1,c2,c3'
INSERT INTO #cd SELECT 10, 'c1'
INSERT INTO #cd SELECT 20, 'c2'
INSERT INTO #cd SELECT 30, 'c3'
So, the lookup is
id cd
10 c1
10 c1
20 c2
30 c3
and, the transactions table has:
cd
c1
c1,c2
c1,c2,c3
I need to replace the codes to their respective IDs, while keeping these in CSV format.
I would like to avoid the cursor because it is too slow. Is there a way to parse the codes, do the JOIN, and recombine the IDs somehow efficiently? I suppose COALESCE may be of use, but need help applying it. Perhaps, there is already a function in t-SQL that does this types of lookups.
The output needs to another column in transactions table:
id
10
10,20
10,20,30

Answer 1

You can first strip out comma into a list and then join and get correct ids for codes and then add them back with commas. I used a row_number upfront to get a unique thing to join back on in my query.
See live demo
CREATE TABLE #t(cd VARCHAR(100))
CREATE TABLE #cd (id INT, cd VARCHAR (1000))
INSERT INTO #t SELECT 'c1'
INSERT INTO #t SELECT 'c1,c2'
INSERT INTO #t SELECT 'c1,c2,c3'
INSERT INTO #cd SELECT 10, 'c1'
INSERT INTO #cd SELECT 20, 'c2'
INSERT INTO #cd SELECT 30, 'c3'
; WITH X AS
(
SELECT
C.id,P1.rn
FROM
(
SELECT *, row_number() over( order by (select 1)) rn,
cast('<X>'+replace(P.cd,',','</X><X>')+'</X>' as XML) AS xmlitems FROM #t P
)P1
CROSS APPLY
(
SELECT fdata.D.value('.','varchar(100)') AS splitdata
FROM P1.xmlitems.nodes('X') AS fdata(D)) O
LEFT JOIN #cd C
ON C.cd= LTRIM(RTRIM(O.splitdata ))
)
SELECT
rn,
id= STUFF((
SELECT ',' + cast(id as varchar(100)) FROM X AS x2
WHERE x2.rn = x.rn
ORDER BY rn FOR XML PATH,
TYPE).value(N'.[1]',N'varchar(max)'), 1, 1, '')
FROM
X
GROUP BY rn
Note: With SQL server 2017 you can also you SPLIT_STRING() function
and STRING_AGG() functions
SQL SERVER 2017 code:
select
id=STRING_AGG(id,',')
from
(
select V=value, rn
from
(
select
rn=row_number() over( order by (select 1)),
cd
from #T
)T
cross apply STRING_SPLIT(cd, ',')
) T
left join #cd C
on cd= v
group by rn