I'm sorry but you just cannot say that "OR is bad" - it being a key part of SQL . It's most likely your use that is bad (e.g. your intermediate result exceeding some cache size).
But "bad performance always due to indexes" gives a hint that you are somewhat new: No, bad performance in my experience was almost always due to developers either not understanding their ORM framework, or writing too expensive queries with or without index. Just adding indexes seldom solved the problem (maybe 1/5 of the time).
But "bad performance always due to indexes" gives a hint that you are somewhat new: No, bad performance in my experience was almost always due to developers either not understanding their ORM framework, or writing too expensive queries with or without index. Just adding indexes seldom solved the problem (maybe 1/5 of the time).