Thank you for the reference... but the Tally table isn't a panacea for all looping problems. The loop here is a process control loop that controls how many times a DELETE is used... I don't believe a Tally table could be used here. If someone can think of a way, please post it because THAT would be truly useful.
Heck, if you can think of a way, write an article on it!
The reasons why
someone would want to do a delete like this has been totally missed...
The purpose of doing looped Deletes is usually two fold...
1. Do the deletes and still allow the table to be used.
2. Keep the transaction log small.
Item #2 above can only be accomplished if the DB is in the simple recovery mode or there is some additional code in the loop that truncates the log while it is running.
The big thing is Item #1... how to do the (massive) deletes and still allow the table to be used by others. For that, you have to have a delay in the loop and you can do that using WAITFOR DELAY '00:00:10'
where the number 10 is some number of seconds. The loop that's listed in the article (and in the thread), whether ROWCOUNT or TOP is used, is fairly agressive and won't necessarily allow other processes to "get in". It's so agressive that you might as well just do the delete all at once. In order for the loop to actually allow other processes to work, the TOP or ROWCOUNT should be small enough to limit any locking to about a second and then the delay should be long enough to allow most other processes to get in and get out... I would think that something between 3 and 10 seconds would be good enough.
Shifting gears a bit... I'm really torn... I very much encourage folks to write articles on this forum... the simple sharing of ideas is what the forum is all about... and, I very much encourage folks that read them to remember that not everyone who can write code can also write a masterpiece article. But, I do feel that there were a large number of points missed in this article and, perhaps, some things in the code that violate what some would consider to be a best practice (you don't need to count loops to do this).
It was pointed out that "For larger tables, where this technique is most effective, you would obviously use larger values for @N and probably constrain on a date column."
What a prime opportunity for several explanations... Why
is this technique most effective for larger tables? Why
would you probably constrain ona a date column? Why
would you want to use larger values for @N?
So, like I said, I'm really torn... I really want people to be encouraged to write without fear of being bashed, but I do have to agree with what some have already said... a bit more thought, a bit more research, and a bit more explanation of the "Why" of "implied points made" would have gone far into turning what should have been a casual script submission into a well written and informative article.
Heh... of course, sometimes it's not actually the article that counts... sometimes the discussions that follow are more useful than the original intent of the article. In that case, this article has more than done it's job.
is pronounced ree-bar and is a Modenism for R
First step towards the paradigm shift of writing Set Based code: Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column.
If you think its expensive to hire a professional to do the job, wait until you hire an amateur. -- Red Adair
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