Re: RPGLESQL - random records from large file

[Charles Wilt <charles.wilt@xxxxxxxxx>]

just a note about Db2's RAND() function
https://stackoverflow.com/questions/36209123/random-function-in-db2-is-not-evenly-distributed/36209627#36209627


I really need to see if that's still the case :)

Charles


On Wed, Oct 2, 2019 at 12:49 PM Booth Martin <booth@xxxxxxxxxxxx> wrote:

> A large file,say a million records in which there are about 12,000
> records with a "W" in Field20.  I want 10 random records from the
> 12000.  I can't figure out how to write the WHERE clause so that only
> records from the 12,000 will be included .
>
> Here's what I use for random hits on the big file:
>
>         exec sql select rand(MICROSECOND(CURRENT_TIMESTAMP)) into :wField5
>             from SYSIBM/SYSDUMMY1;
>         wSeed = wField5 * 10000;
>         //
> ---------------------------------------------------------------------
>         // Get 10 random numbers
>         clear wCount;
>         wNdx = 0;
>         dow wNdx < 10 and wCount < 1200;  // (if we can't get 10 in
> 1200, bail)
>           wCount += 1;
>           exec sql select rand(:wSeed) into :wField5
>             from SYSIBM/SYSDUMMY1;
>           wSeed = wField5 * 10000;
>           exec sql select FIELD1 into :wField1
>                      from FILE01
>                      where rrn(FILE01) = :wSeed;
>
> ...
>
> "where rrn(FILE01) = :wSeed and FIELD20 = 'W';" seems easy but somehow
> wrong.
>
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