How to Add an Exception to a SQL 'Quality Check' Rule?

I have the following query:

SELECT A.ID, A.FUND, B.MANAGER_NAME, C.FUND, C.MGR_NM
FROM TABLE_1 A 
LEFT JOIN TABLE_2 B ON  
            A.ID = B.ID
LEFT JOIN REFERENCE_TABLE C ON
A.FUND = C.FUND
WHERE 
B.MANAGER_NAME != C.MGR_NM

The results of this query show when a Manager is incorrectly assigned to a fund.

The REFERENCE_TABLE is the source of truth and shows the correct FUND and MGR_NM assignments. However, I need to add one exception to this rule: when FUND = 'BOSTON', it's okay if MANAGER_NAME = 'Kim, John, or Danny'.

All other funds have a 1:1 relationship between fund and manager name.
How can I add this exception to my query?

> Show all results where MANAGER_NAME does not match MGR_NM, unless the FUND is 'BOSTON', then it is okay if MANAGER_NAME is one of 'Kim, John, or Danny'

Sounds like a case for a simple OR expression in your criteria, but we need to invert the match on 'Kim, John, or Danny' and return if the fund is 'BOSTON' and the MANAGER_NAME is NOT one of 'Kim, John, or Danny'

But it's not too simple, be careful when injecting OR operator into your criteria though, if you are not using brackets to separate the logical expressions in the criteria then OR will compare either side of the operator independently which can produce undesirable results.

In the following solution no brackets are used, but we have to evaluate a non-match for the BOSTON fund in the original logic so that 'Kim', 'John', 'Danny' are not considered valid for other funds:

SELECT A.ID, A.FUND, B.MANAGER_NAME, C.FUND, C.MGR_NM
FROM TABLE_1 A 
LEFT JOIN TABLE_2 B ON A.ID = B.ID
LEFT JOIN REFERENCE_TABLE C ON A.FUND = C.FUND
WHERE 
A.FUND <> 'BOSTON' 
AND B.MANAGER_NAME != C.MGR_NM
OR A.FUND = 'BOSTON' 
   AND B.MANAGER_NAME != C.MGR_NM 
   AND B.MANAGER_NAME NOT IN ('Kim', 'John', 'Danny')

You might prefer to use brackets to make the expression more readable, or to highlight the exceptional case. The RDBMS is likely to expand the brackets on evaluation anyway so it shouldn't have an impact on performance either way, but it does allow us to use syntax like this if it is helpful:

SELECT A.ID, A.FUND, B.MANAGER_NAME, C.FUND, C.MGR_NM
FROM TABLE_1 A 
LEFT JOIN TABLE_2 B ON A.ID = B.ID
LEFT JOIN REFERENCE_TABLE C ON A.FUND = C.FUND
WHERE 
B.MANAGER_NAME != C.MGR_NM
AND (
    A.FUND <> 'BOSTON' 
    OR A.FUND = 'BOSTON' 
       AND B.MANAGER_NAME NOT IN ('Kim', 'John', 'Danny')
    )

While this should work, the question is why are 'Kim', 'John', 'Danny' valid? If REFERENCE_TABLE is the source of truth then you could allow multiple entries for each fund in this table, then you wouldn't need to hardcode the specific case for 'BOSTON' at all and we can use an OUTER JOIN to return only the non-correlated rows:

SELECT A.ID, A.FUND, B.MANAGER_NAME, C.FUND, C.MGR_NM
FROM TABLE_1 A 
LEFT JOIN TABLE_2 B ON A.ID = B.ID
LEFT OUTER JOIN REFERENCE_TABLE C ON A.FUND = C.FUND 
                                  AND B.MANAGER_NAME = C.MGR_NM
WHERE 
C.FUND IS NULL

This works because all the valid manager will match and will have a non-null value for C.FUND. However all rows that do not find a corresponding match in the REFERENCE_TABLE will have a value of null for C.FUND, these are the rows that we want to see.