Chapter 11. Advanced Searching
In a very real sense, this entire book so far has been about searching. You’ve seen all sorts of queries that use joins and WHERE clauses and grouping techniques to search out and return the results that you need. Some types of searching operations, though, stand apart from others in that they represent a different way of thinking about searching. Perhaps you’re displaying a result set one page at a time. Half of that problem is to identify (search for) the entire set of records that you want to display. The other half of that problem is to repeatedly search for the next page to display as a user cycles through the records on a display. Your first thought may not be to think of pagination as a searching problem, but it can be thought of that way, and it can be solved that way; that is the type of searching solution this chapter is all about.
11.1. Paginating Through a Result Set
You want to paginate or “scroll through” a result set. For example, you want to return the first five salaries from table EMP, then the next five, and so forth. Your goal is to allow a user to view five records at a time, scrolling forward with each click of a “Next” button.
Because there is no concept of first, last, or next in SQL, you must impose order on the rows you are working with. Only by imposing order can you accurately return ranges of records.
DB2, Oracle, and SQL Server
Use the window function ROW_NUMBER OVER to impose order, and specify the window of ...