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copied!<p>An index is a PHYSICAL DATA STRUCTURE which is used to help speed up retrieval type queries; it's not simply a table upon a table -> good for a concept though. Another concept is the way indexes work at the back of your text book (the only difference is with your book a search key could point to multiple pages / matches whereas with indexes a search key points to only one page/match). An index is defined by data structures so you could use a B+ tree index and there are even hash indexes. It's Database/Query optimization from the physical/internal level of the Database - I'm assuming that you know that you're working at the higher levels of the DBMS which is easier. An index is rooted within the internal levels and that make DB query optimization much more effective and interesting.</p> <p>I've noticed from your question that you have not even developed the query as yet. Focus on the query first. Indexing comes after, as a matter of a fact, in any graduate or post graduate Database course, indexing falls under the maintenance of a Database and not necessarily the development.</p> <p>Also N.B. I have seen quite many people say as a rule to make all primary keys indexes. This is not true. There are many instances where a primary key index would slow up the Database. Infact, if we were to go with only primary indexes then should use hash indexes since they work better than B+ trees!</p> <p>In summary, it doesn't make sense to ask a question for a query and an index. Ask for help with the query first. Then given your tables (relational schema) and SQL query, then and only then could I advice you on the best index - remember its maintenance. We can't do maintanance if there is 0 development.</p> <p>Kind Regards,</p> <p>N.B. most questions concerning indexes at the post graduate level of many computing courses are as follows: we give the students a relational schema (i.e. your tables) and a query and then ask: critically suggest a suitable index for the following query on the tables ----> we can't ask a question like this if they dont have a query</p>

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