Multiple IN statements for WHERE. Would this return good data?

Question

SELECT ['VISA CK  - 021810$'].[ACCT NBR     #1], ['VISA CK  - 021810$'].[ALT CUST NM  #1], ['VISA CK  - 021810$'].[LAST USED]
FROM ['VISA CK  - 021810$']
WHERE ['VISA CK  - 021810$'].[ALT CUST NM  #1] 
    IN (
        SELECT ['VISA CK  - 021810$'].[ALT CUST NM  #1]
        FROM ['VISA CK  - 021810$']
        GROUP BY ['VISA CK  - 021810$'].[ALT CUST NM  #1]
            HAVING COUNT(['VISA CK  - 021810$'].[ALT CUST NM  #1]) > 1
        )
    AND ['VISA CK  - 021810$'].[ACCT NBR     #1]
    IN (
        SELECT ['VISA CK  - 021810$'].[ACCT NBR     #1]
        FROM ['VISA CK  - 021810$']
        GROUP BY ['VISA CK  - 021810$'].[ACCT NBR     #1]
            HAVING COUNT(['VISA CK  - 021810$'].[ACCT NBR     #1]) > 1
        )

Answer 1

It is a valid SQL construct but we can't comment on whether it works or not.

You are saying: for each row in ['VISA CK - 021810$'], return this row if I find matches for both [ACCT NBR #1] and [ALT CUST NM #1] in their relative IN clauses

Answer 2

Yes, it would return good data. The WHERE clause will assure that both IN clauses are respected before returning any data as you're using an AND.

Answer 3

Rewritten using JOINs:

SELECT t.[ACCT NBR     #1], 
       t.[ALT CUST NM  #1], 
       t.[LAST USED]
  FROM ['VISA CK  - 021810$'] t
  JOIN (SELECT ['VISA CK  - 021810$'].[ALT CUST NM  #1]
          FROM ['VISA CK  - 021810$']
      GROUP BY ['VISA CK  - 021810$'].[ALT CUST NM  #1]
        HAVING COUNT(['VISA CK  - 021810$'].[ALT CUST NM  #1]) > 1) x ON x.[ALT CUST NM  #1] =   t.[ALT CUST NM  #1] 
  JOIN (SELECT ['VISA CK  - 021810$'].[ACCT NBR     #1]
          FROM ['VISA CK  - 021810$']
      GROUP BY ['VISA CK  - 021810$'].[ACCT NBR     #1]
        HAVING COUNT(['VISA CK  - 021810$'].[ACCT NBR     #1]) > 1) y ON y.[ACCT NBR     #1] = t.[ACCT NBR     #1]

Make sure it returns the data you expect - tune after that. Assuming the query you provided is correct, JOINs are generally preferred over subqueries but reviewing and comparing the Execution Plan will tell you what is best for your situation.