b-tree-index

Newbie database index question

I have a table with multiple indexes, several of which duplicate the same columns: Index 1 columns: X, B, C, D Index 2 columns: Y, B, C, D Index 3 columns: Z, B, C, D I'm not very knowledgeable on indexing in practice, so I'm wondering if somebody can explain why X, Y and Z were paired with these same columns. B is an effective date....

Databases and B+Trees indexes

Where can I find information on whether which databases are using B+Trees over B-Trees for their index implementations? Oracle appears to be using B+Trees. Although they don't describe it on their documentation, their graphics appear to be pointing that B+Trees are actually being used. ...