I have a single table where I need to query based on 4 columns a,b,c,d The most common query will be a select based on all 4 columns at the same time, however I need to be able to search quickly for each of the columns taken separately, or also combinations of them (e.g. a&b, a&d, b&c&d and so on). Shall I create an index for every combination? or it's better to have only an index for a&b&c&d and one for a, one for b, one for c, one for d? in this last case a query that matches only a&b for example will be sped up because both a and be have an index?