Do you know the difference between a list and a hash table? Hopefully yes. When there is no index, the database is stored in a list. You look for something, yo

Do you know the difference between a list and a hash table? Hopefully yes. When there is no index, the database is stored in a list. You look for something, you have to go through every item. When there is an index, the databases uses a hash table to reference the locations of items. You look for something, you get the location instantly. It's really simple. There are more types of structures: trees, hash tables, bimap, arrays, etc... with different performance characteristics.