Hi!
>From: Tom Crimmins <mysql2@stripped>
>To: sguazt sguazt <sguazt@stripped>
>CC: mysql@stripped
>Subject: RE: Queries inside UDF
>Date: Wed, 16 Mar 2005 10:09:16 -0600
>
...
>
>Can you explain exactly what you are using this for? What benefit does this
>provide over just executing the query?
>
>You can either execute SELECT foobar() or SELECT COUNT(*) FROM tblfoobar,
>and
>you don't have to do anything to make the latter work. Creating the UDF
>just
>
>seems like a lot of extra work. Maybe this is my ignorance, but I don't see
>much use for executing a query within a UDF esspecially if you are using
>4.1
>
>with subqueries.
ok sorry if I submitted a stupid exampe :P
but I wanted to keep the stuff simple.
My real case is a little more complicated ...
First of all, unfornately I've to use MySQL 4.0.21.
The purpose of creating a UDF, in my case, is doing something that in my
opinion cannot be done in a query.
For example, if you have to implement in SQL the following pseudo-code:
start = <a unix timestamp>;
duration = 100;
stop = null;
increment = 0;
while ( true ) {
start2 = 0;
stop2 = 0;
stop = start + ( duration - increment );
rs = doQuery( "SELECT start,stop FROM t1 INNER JOIN t2 ON t1.c1=t2.c1 ....
WHERE t1.start>=" + start + " AND t1.stop<=" + stop );
if ( rs == null ) {
delta = 0;
start2 = rs[0]['start'];
stop2 = rs[0]['stop'];
if ( start < start2 ) {
delta += start2 - start;
}
increment += delta;
start = stop2
}
else {
break;
}
}
return stop;
what do you write?
The main problem is that you can establish a-priori when you stop the main
while ... :(
I thought to use a temporary table but the problem remains ...
Furthermore that code produces an info that is to be used by another (more
complex) query.
So the only solutions are:
1. use a high-level language (C,perl,Java,PHP) and implement the entire
logic (not only the code above) in that language (but this seems to be too
slow ... I did it before exploring the UDF world ;) )
2. try to write a UDF that implement the code above; so you create a UDF,
e.g. named foobar, you can use inside other query: SELECT ...,foobar( start,
duration ) AS stop FROM <a very long JOIN> ...
Any idea?
bye!!!
-- Marco
>--
>Tom Crimmins
>Interface Specialist
>Pottawattamie County, Iowa
>
>--
>MySQL General Mailing List
>For list archives: http://lists.mysql.com/mysql
>To unsubscribe: http://lists.mysql.com/mysql?unsub=1
>
_________________________________________________________________
Ricerche online più semplici e veloci con MSN Toolbar!
http://toolbar.msn.it/
