Search child rows for values - sql-server

Question

I have something like this:
Transaction Customer
1 Cust1
2 Cust2
3 Cust3
4 Cust4
TransID Code
2 A
2 B
2 D
3 A
4 B
4 C
If I want to be able to do something like "IF Customer 'Cust1' Has code 'A'", how should I best build a view? I want to end up being able to query something like "Select Customer from View where Code in [Some list of codes]" OR "Select Cust1 from View Having Codes in [Some list of codes]"
While I can do something like
Customer | Codes
Cust1 | A, B, D
Etc.
SELECT Transaction from Tbl where Codes like 'A'
This seems to me to be an impractical way to do it.

Answer 1

Here's how I'd do it
;with xact_cust (xact, cust) as
(
select 1, 'cust1' union all
select 2, 'cust2' union all
select 3, 'cust3' union all
select 4, 'cust4'
), xact_code (xact, code) as
(
select 2, 'A' union all
select 2, 'B' union all
select 2, 'D' union all
select 3, 'A' union all
select 4, 'B' union all
select 4, 'C'
)
select Cust, Code
from xact_cust cust
inner join xact_code code
on cust.xact = code.xact
where exists (select 1
from xact_code i
where i.xact = code.xact
and i.code = 'A')
If you NEED the codes serialized into a delimited list, take a look at this article: What this query does to create comma delimited list SQL Server?

Answer 2

Here's another option...
IF OBJECT_ID('tempdb..#CustomerTransaction', 'U') IS NOT NULL
DROP TABLE #CustomerTransaction;
CREATE TABLE #CustomerTransaction (
TransactionID INT NOT NULL PRIMARY KEY,
Customer CHAR(5) NOT NULL
);
INSERT #CustomerTransaction (TransactionID, Customer) VALUES
(1, 'Cust1'), (2, 'Cust2'), (3, 'Cust3'),
(4, 'Cust4'), (5, 'Cust5');
IF OBJECT_ID('tempdb..#TransactionCode', 'U') IS NOT NULL
DROP TABLE #TransactionCode;
CREATE TABLE #TransactionCode (
TransactionID INT NOT NULL,
Code CHAR(1) NOT NULL
);
INSERT #TransactionCode (TransactionID, Code) VALUES
(2, 'A'), (2, 'B'), (2, 'D'), (3, 'A'), (4, 'B'), (4, 'C');
--SELECT * FROM #CustomerTransaction ct;
--SELECT * FROM #TransactionCode tc;
--=============================================================
SELECT
ct.TransactionID,
ct.Customer,
CodeList = STUFF(tcx.CodeList, 1, 1, '')
FROM
#CustomerTransaction ct
CROSS APPLY (
SELECT
', ' + tc.Code
FROM
#TransactionCode tc
WHERE
ct.TransactionID = tc.TransactionID
ORDER BY
tc.Code ASC
FOR XML PATH('')
) tcx (CodeList);
Results...
TransactionID Customer CodeList
------------- -------- -----------
1 Cust1 NULL
2 Cust2 A, B, D
3 Cust3 A
4 Cust4 B, C
5 Cust5 NULL