Oracle Equivalent of MySQL's LIMIT (Or how to page results in Oracle)

I'm really just posting this for my own benefit but if you're reading this and it has been helpful, drop me a comment to let me know.

SELECT
  *
FROM (
  SELECT 
    a.*,
    ROW_NUMBER() OVER (ORDER BY column_to_sort) rn
  FROM
    my_table a
  WHERE
    my_column_to_filter = 'my_value_to_filter'
 )
WHERE
  rn >= my_starting_row AND rn <= my_ending_row

Evaluating Backreferences in Oracle REGEXP_REPLACE

Here's the problem. I want to use Oracle's REGEXP_REPLACE function to replace a string of digits with a zero-padded string. In Perl I would do it like this:

#--- Change xyz123 to xyz000123
my $string = "xyz123";
$string =~ s/(\d+)$/sprintf("%06d", $1)/e;

So here is what I started with in Oracle PL/SQL:

my_string := 'xyz123'
regexp_replace(my_string, '(\d+)$', lpad('\1', 6, 0));

And what I got was xyz0000123. What I discovered was that the LPAD function was being evaluated before the backreference (\1) was. So no matter what I did, the LPAD function always saw the string to be padded as 2 characters long.

So to get around this, I wrote another function called evalpad. With this, I do the replacement in 2 steps. The first is to replace the string with an embedded pad psuedo-function. Then I call a second function to do the actual replacement. Here's the code:

create or replace function evalpad (
  strIn in varchar
)
return
  varchar
as
  retval varchar(255);
  arg1 varchar(50);
  arg2 varchar(50);
  padded_number varchar(100);
begin
  retval := strIn;
  while (regexp_instr(retval, 'pad\((\d+)') > 0) loop
    arg1 := regexp_substr(retval, 'pad\((\d+)');
    arg1 := regexp_replace(arg1, 'pad\(', '');
    arg2 := regexp_substr(retval, 'pad\((\d+),\s*(\d+)');
    arg2 := regexp_replace(arg2, 'pad\((\d+),\s*', '');
    padded_number := lpad(arg1, arg2, 0);
    retval := regexp_replace(retval, 'pad\((\d+),\s*(\d+)\)', padded_number, 1, 1);
  end loop;
  return retval;
end;

Then in my original function I do this:

my_string := 'xyz123'
regexp_replace(my_string, '(\d+)$', 'pad(\1, 6)');
my_string := evalpad(my_string);

Catching and Logging JavaScript Errors

As browser-based applications become more JavaScript centric, it becomes harder to debug user issues. For years I have been logging and handling server side errors, but only recently have I started logging JavaScript errors. And it turns out the solution was very simple.

First, the JavaScript code. Near the top of my main JavaScript file that I include on every page of my application, I put this code that I found online and modified for my own use. I should note here that I am using jQuery (and you should to).

window.onerror = function(m,u,l){
    $.post(
        basePath + "/js_error.cfm", 
        {
            msg: m,
            url: u,
            line: l,
            window: window.location.href
        }
    );
    return true;
}

All this code is doing is catching untrapped errors and posting them to a page on the server. Now for the server-side code:

    


#errorReport#

The ColdFusion script write the error to a log file and then emails me the report.

For now this will blindly send me error reports in the background. But in the future I would like to pop up a form to the user to get more information such as asking what they were trying to do when they got the error. I built a prototype using the jQuery UI dialog module. However, I need to work out some more UX questions like:
- How often do I ask for input especially if it's an error they are getting on every page?
- Should I pilot this dialog to select users first?
- Would a live chat with tech support be an option (using web sockets)?