CST363.5 Module 5

 CST363.5 Module 5

If indexes are supposed to speed up performance of query,  what does the author mean by a slow index? 

there are certain conditions in which a query may take longer than expected, specifically in the case that the query calls for more than one entry or row, tree traversal must be re-iterated for each qualifying entry and then access the table per each indicated index. I think the intention behind it is that under certain conditions it may be faster or more efficient to do a table scan, specifically if the query is of a large range, otherwise using an index scan may require more time than necessary.