---- Message from mailto:m...@sai.msu.ru "Sergey E. Koposov" m...@sai.msu.ru at 05-04-2010 06:36:23 PM ------
Hello, I'm getting strange results with PostgreSQL random() function. It would be great if someone could either show where I am wrong or PG is wrong. Here is what I do (PG 8.4.3, x86_64 platform); I basically try to create the table with the column filled with random numbers (either integer or doubles). And I'm getting too many collisions. Here is the SQL code: ----------------------- begin; select setseed(0); create temporary table tmpx1 as select ((random())) as id from generate_series(1,100000); select id ,count(*) from tmpx1 group by (id) having count(*)1; ***snip** Random() does not guarantee the results will not repeat. its just like rolling dice every time the dice rolls its an independent result so it will repeat at some point, so every time Random() is called its an independent event that has no idea about past results. You are calling random 100,000 times. To create a random list of numbers that don't repeat you have to filter the repeated values out one at a time, with another function. Tip trying to use sql to filter out duplicated values will sort the result set first before filtering duplicates resulting in a not so random list of numbers. All legitimate Magwerks Corporation quotations are sent in a .PDF file attachment with a unique ID number generated by our proprietary quotation system. Quotations received via any other form of communication will not be honored. CONFIDENTIALITY NOTICE: This e-mail, including attachments, may contain legally privileged, confidential or other information proprietary to Magwerks Corporation and is intended solely for the use of the individual to whom it addresses. If the reader of this e-mail is not the intended recipient or authorized agent, the reader is hereby notified that any unauthorized viewing, dissemination, distribution or copying of this e-mail is strictly prohibited. If you have received this e-mail in error, please notify the sender by replying to this message and destroy all occurrences of this e-mail immediately. Thank you.
