Fastest most/efficient way to do pagination with SQL searching DB2

Question

Right now I do two separate SQL statements, one doing a SELECT COUNT(*) on basically the same criteria as the search statement. I am not the best at making thes

Answer 1

If you're trying to display a total count of the results alongside the paginated counts (so '0 to 25 out of 38), a separate statement may be your best bet. I've tried a number of things to get the counts alongside the individual rows, but the performance (even over a moderate test database) is terrible.

What you probably ought to do is create a view you can query against, which contains all your selection criteria, then just wrap it with the necessary behaviour:
Count:

SELECT COUNT(*)
FROM view

Ranked rows:

SELECT *
FROM (SELECT *, ROW_NUMBER() OVER(ORDER BY item) as RANK
      FROM view) as TEMP
WHERE RANK BETWEEN 0 AND 25

You will of course need to add the relative where conditions, but this is the type of thing views are meant to handle.

If you don't actually need to know the total rows ahead of time, you can simply set the end-rank as the start-rank plus some offset. Then, when you display your results with PHP, simply edit the ending display value.

Some random notes: 1) Is there are reason that line isn't upper()d?
2) The performance of this query is going to suffer almost no matter what you do, simply because of all the string manipulation/comparisons. Is it possible to eliminate or ignore some of the conditions? Unless the indicies used over the various string columns have had upper applied to them (some later versions of DB2 allow certain scalar functions to be applied to the index key), most indicies are going to be completely useless (it doesn't help that you're looking for %ANYTHING% after all).

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Okay, there is a 'tricky' way to do something like this, and seems to get okay performance... Try something like this (a view defined first will really help):

SELECT TEMP.*, CASE WHEN RANK = 0 THEN (SELECT COUNT(*)
                                        FROM view)
                    ELSE 0 END
FROM (SELECT *, ROW_NUMBER() OVER(ORDER BY item) as RANK
      FROM view) as TEMP
WHERE RANK BETWEEN 0 AND 25

Of course, you'll still have to have your where clause defined in the subselect too...