Re: Inserting Multiple Random Rows - Mailing list pgsql-sql

That won't work because Order by does not recompute Random() once gets a 
number it  stops

you need to generate a series of random numbers then select each record 
one at a time out of cities table .  You will have to write a plsql 
function to do this As any join will cause the result to be ordered.

Here is example of pl-sql procedure that inserts records randomly into a 
table from a another table.  This is an  excerpt from the function.  
There is more logic that limits the random result set size and  rules 
not to repeat a given number.

--First create cursor of the source records    OPEN _questions SCROLL for  (Select  *    from questions
          where quest_expire > now()::date                                and trim( both '' from quest_type)  = 
 
_classexams.exam_quest_type                                and trim( both '' from quest_level) = 
_classexams.exam_level                            order by quest_id );

--need to limit the number range created by random so not to exceed the 
record count created by the Cursor
select count(quest_id) into _rcount from educate.questions                where quest_expire > now()::date
     and trim( both '' from quest_type)  = 
 
_classexams.exam_quest_type                    and trim( both '' from quest_level) = 
_classexams.exam_level ;

Generate a Random list of  of numbers
for _randlist IN (Select num from (                select round(random()*1000)::int as num from 
generate_series(1,100000)) rand                where num <= _rcount and num > 0 ) LOOP

FETCH ABSOLUTE _randlist.num from _questions into _quest ;

Next Insert into Into the destination  Table

end loop;

On 4/28/2010 12:22 PM, Gary Chambers wrote:
> All,
>
> I have a table of user addresses that I'm trying to randomly populate
> with data from a cities table.  Using the following query:
>
> INSERT INTO useraddrs(userid, addrdesc, city, stprov)
> SELECT u.userid, 'Home', c.cityname, c.stateabbr
> FROM users u, cities c
> WHERE u.userid NOT IN (SELECT userid FROM useraddrs)
>      AND cid=(SELECT cid FROM cities ORDER BY RANDOM() LIMIT 1);
>
> I am able to achieve most of what I am trying to accomplish, but once
> the random number is selected, it doesn't change.  What am I missing?
> Thank you in advance.
>
> -- Gary Chambers
>
> /* Nothing fancy and nothing Microsoft! */
>
>    


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