COALESCE Vs OR IS NULL

I would like to know for my scenario, if there are 2 tables:

employee: id, city, job_level

filters: city, job_level, some_val

I have a query like:

SELECT * 
FROM   employee e 
WHERE  NOT EXISTS(SELECT 1 
                  FROM   filters f 
                  WHERE  e.city = COALESCE(f.city, e.city) 
                         AND ( f.job_level IS NULL 
                                OR e.job_level = f.job_level )) 

If you can see the conditions for both city and job_level work exactly the same way. However, I would like to know which one would perform better. Also, I would like to know the recommended indexes for these tables for such a query.

It isn't going to really make a difference from a performance perspective. You have a complicated WHERE clause, that already includes an OR condition. This pretty much precludes using an index.

Given what you are doing with the COALESCE(), I think OR IS NULL is clearer.

If you care about performance, you might consider splitting this into multiple comparisons:

WHERE NOT EXISTS (SELECT 1 
                  FROM filters f 
                  WHERE e.city = f.city AND 
                        ( f.job_level IS NULL  OR e.job_level = f.job_level )
                 ) AND
      NOT EXISTS (SELECT 1 
                  FROM filters f 
                  WHERE f.city IS NULL AND 
                        ( f.job_level IS NULL  OR e.job_level = f.job_level )
                 ) 

This can at least take advantage of an index on filters(city, job_level).