How do I match a substring of variable length? - sql-server

Question

I am importing data into my SQL database from an Excel spreadsheet.
The imp table is the imported data, the app table is the existing database table.
app.ReceiptId is formatted as "A" followed by some numbers. Formerly it was 4 digits, but now it may be 4 or 5 digits.
Examples:
A1234
A9876
A10001
imp.ref is a free-text reference field from Excel. It consists of some arbitrary length description, then the ReceiptId, followed by an irrelevant reference number in the format " - BZ-0987654321" (which is sometimes cropped short, or even missing entirely).
Examples:
SHORT DESC A1234 - BZ-0987654321
LONGER DESCRIPTION A9876 - BZ-123
REALLY LONG DESCRIPTION A2345 - B
REALLY REALLY LONG DESCRIPTION A23456
The code below works for a 4-digit ReceiptId, but will not correctly capture a 5-digit one.
UPDATE app
SET
[...]
FROM imp
INNER JOIN app
ON app.ReceiptId = right(right(rtrim(replace(replace(imp.ref,'-',''),'B','')),5)
+ rtrim(left(imp.ref,charindex(' - BZ-',imp.ref))),5)
How can I change the code so it captures either 4 (A1234) or 5 (A12345) digits?

Answer 1

As ughai rightfully wrote in his comment, it's not recommended to use anything other then columns in the on clause of a join.
The reason for that is that using functions prevents sql server for using any indexes on the columns that it might use without the functions.
Therefor, I would suggest adding another column to imp table that will hold the actual ReceiptId and be calculated during the import process itself.
I think the best way of extracting the ReceiptId from the ref column is using substring with patindex, as demonstrated in this fiddle:
SELECT ref,
RTRIM(SUBSTRING(ref, PATINDEX('%A[0-9][0-9][0-9][0-9]%', ref), 6)) As ReceiptId
FROM imp
Update
After the conversation with t-clausen-dk in the comments, I came up with this:
SELECT ref,
CASE WHEN PATINDEX('%[ ]A[0-9][0-9][0-9][0-9][0-9| ]%', ref) > 0
OR PATINDEX('A[0-9][0-9][0-9][0-9][0-9| ]%', ref) = 1 THEN
SUBSTRING(ref, PATINDEX('%A[0-9][0-9][0-9][0-9][0-9| ]%', ref), 6)
ELSE
NULL
END As ReceiptId
FROM imp
fiddle here
This will return null if there is no match,
when a match is a sub string that contains A followed by 4 or 5 digits, separated by spaces from the rest of the string, and can be found at the start, middle or end of the string.

Answer 2

Try this, it will remove all characters before the A[number][number][number][number] and take the first 6 characters after that:
UPDATE app
SET
[...]
FROM imp
INNER JOIN app
ON app.ReceiptId in
(
left(stuff(ref,1, patindex('%A[0-9][0-9][0-9][0-9][ ]%', imp.ref + ' ') - 1, ''), 5),
left(stuff(ref,1, patindex('%A[0-9][0-9][0-9][0-9][0-9][ ]%', imp.ref + ' ') - 1, ''), 6)
)
When using equal, the spaces after is not evaluated