fuzzy join in SQL - sql

Question

I was hoping someone could shed some light for me on my issue.
I need to be able to join the following two tables together in SQL
Values in table 1 for some column
QWERTY10
QAZWSXEDCR10
QAZWSXED1230
Values in table 2 for some column
QWWERTY20
QAZWSXEDCR20
QAZWSXED1240
the result that I need is
QWERTY100000 QWERTY200000
QAZWSXEDCR10 QAZWSXEDCR20
QAZWSXED1230 QAZWSXED1240
Now, for QWERTY10000 to be linked to QWERTY20000 I need to do the join on the first 6 characters of the value in the field
but for the QAZWSXEDCR10 to be linked to QAZWSXEDCR20 I need to do a join on the first 10 characters of the value in the field. If I do a join on the first 6 characters only then I will get duplicates. I will have smth like this:
QAZWSXEDCR10 QAZWSXEDCR20
QAZWSXEDCR10 QAZWSXED1240
QAZWSXED1230 QAZWSXEDCR20
QAZWSXED1230 QAZWSXED1240
and I also need QAZWSXED1230 to be linked to QAZWSXED1240 and there I need to do a join on 8 characters to make it work.
im having a hard time to figure out how to join my data together. I would like to avoid doing 10 different joins each based on a different number of characters.
eg do a join on 6 characters first and if not successful then do the join on 7, 8, 9 and 10. - there must be a different way...
Can someone recommend a solution here?
KR

Answer 1

As mentioned in Milney's comment, PatIndex may help by finding the string location of the first number - or special character if applicable. You can then construct a substring of the matching portions of the strings
select table1.col as col1,
table2.col as col2
from table1
inner join
table2
on substring( table1.col, 1, patindex( '[0-9]', table1.col ) ) =
substring( table2.col, 1, patindex( '[0-9]', table2.col ) )

Answer 2

This is a modification of Alex's answer, just to handle the case where one or both values do not contain a digit:
select t1.col as col1, t2.col as col2
from table1 t1 inner join
table2 t2
on left(t1.col, patindex('%[0-9]%', t1.col+'0')) = left(t2.col, patindex('%[0-9]%', t2.col+'0'));

Answer 3

I Think this will help
Create table #table1 ( strValue varchar(100) )
Create table #table2 ( strValue varchar(100) )
Insert Into #table1 ( strValue ) Values
('QWERTY10'), ('QAZWSXEDCR10'),('QAZWSXED1230')
Insert Into #table2 ( strValue ) Values
('QWERTY20'), ('QAZWSXEDCR20'),('QAZWSXED1240')
Declare #MaxlengthT1 int, #MaxlengthT2 int
SELECT #MaxlengthT1 = MAX(LEN(strValue)) FROM #table1
SELECT #MaxlengthT2 = MAX(LEN(strValue)) FROM #table2
select a.strValue + REPLICATE('0',#MaxlengthT1 - LEN(a.strValue)) as col1,
b.strValue + REPLICATE('0',#MaxlengthT1 - LEN(b.strValue)) as col2
from #table1 a
inner join
#table2 b
on substring( a.strValue, 0, patindex( '%[0-9]%', a.strValue )) =
substring( b.strValue, 0, patindex( '%[0-9]%', b.strValue ))
DROP TABLE #table1
DROP TABLE #table2