In relational databases say Oracle or Sybase there is only one primary key for a given table. So by definition you can have one primary key on any table consists of one column or composite primary key (multiple columns).
Please check threads on “ORC files and statistics” in this forum.for detailed explanation. HTH Dr Mich Talebzadeh LinkedIn https://www.linkedin.com/profile/view?id=AAEAAAAWh2gBxianrbJd6zP6AcPCCdOABUrV8Pw Sybase ASE 15 Gold Medal Award 2008 A Winning Strategy: Running the most Critical Financial Data on ASE 15 http://login.sybase.com/files/Product_Overviews/ASE-Winning-Strategy-091908.pdf Author of the books "A Practitioner’s Guide to Upgrading to Sybase ASE 15", ISBN 978-0-9563693-0-7. co-author "Sybase Transact SQL Guidelines Best Practices", ISBN 978-0-9759693-0-4 Publications due shortly: Complex Event Processing in Heterogeneous Environments, ISBN: 978-0-9563693-3-8 Oracle and Sybase, Concepts and Contrasts, ISBN: 978-0-9563693-1-4, volume one out shortly http://talebzadehmich.wordpress.com <http://talebzadehmich.wordpress.com/> NOTE: The information in this email is proprietary and confidential. This message is for the designated recipient only, if you are not the intended recipient, you should destroy it immediately. Any information in this message shall not be understood as given or endorsed by Peridale Technology Ltd, its subsidiaries or their employees, unless expressly so stated. It is the responsibility of the recipient to ensure that this email is virus free, therefore neither Peridale Technology Ltd, its subsidiaries nor their employees accept any responsibility. From: Philip Lee [mailto:philjj...@gmail.com] Sent: 01 February 2016 15:49 To: user@hive.apache.org Subject: Re: ORC format What do you mean by the silver bullet? so you mean it is not that stored as primary key on each column. It is just stored as storage indexing, right? "The statistics helps the optimiser. So whether one table or many, the optimiser will take advantage of stats to push down the predicate for faster decision." I understand this sentence when the operating tree is consisted of filter function because when facing a filter function, it can skip the unrelated rows. but do you think its aspect can be beneificial on joining two tables as well? On Mon, Feb 1, 2016 at 4:43 PM, Mich Talebzadeh <m...@peridale.co.uk <mailto:m...@peridale.co.uk> > wrote: Hi, Orc table use what is known as storage index with stats (min, max. sum etc) stored at the table, stripe and rowindex (rows of 10K batches) level. The statistics helps the optimiser. So whether one table or many, the optimiser will take advantage of stats to push down the predicate for faster decision. Again ORC table is not a silver bullet. It can be valuable when conditions are met. HTH. Dr Mich Talebzadeh LinkedIn https://www.linkedin.com/profile/view?id=AAEAAAAWh2gBxianrbJd6zP6AcPCCdOABUrV8Pw Sybase ASE 15 Gold Medal Award 2008 A Winning Strategy: Running the most Critical Financial Data on ASE 15 http://login.sybase.com/files/Product_Overviews/ASE-Winning-Strategy-091908.pdf Author of the books "A Practitioner’s Guide to Upgrading to Sybase ASE 15", ISBN 978-0-9563693-0-7. co-author "Sybase Transact SQL Guidelines Best Practices", ISBN 978-0-9759693-0-4 Publications due shortly: Complex Event Processing in Heterogeneous Environments, ISBN: 978-0-9563693-3-8 Oracle and Sybase, Concepts and Contrasts, ISBN: 978-0-9563693-1-4, volume one out shortly http://talebzadehmich.wordpress.com <http://talebzadehmich.wordpress.com/> NOTE: The information in this email is proprietary and confidential. This message is for the designated recipient only, if you are not the intended recipient, you should destroy it immediately. Any information in this message shall not be understood as given or endorsed by Peridale Technology Ltd, its subsidiaries or their employees, unless expressly so stated. It is the responsibility of the recipient to ensure that this email is virus free, therefore neither Peridale Technology Ltd, its subsidiaries nor their employees accept any responsibility. From: Philip Lee [mailto:philjj...@gmail.com <mailto:philjj...@gmail.com> ] Sent: 01 February 2016 15:21 To: user@hive.apache.org <mailto:user@hive.apache.org> Subject: ORC format Hello, I experiment the performance of some systems between ORC and CSV file. I read about ORC documentation on Hive website, but still curious of some things. I know ORC format is faster on filtering or reading because it has indexing. Has it advantage of joining two tables of ORC dataset as well? Could you explain about it in detail? When experimenting, it seems like it has some advantages of joining in some aspect, but not quite sure what characteristic of ORC make this happening rather than CSV. Best, Phil -- ========================================================== Hae Joon Lee Now, in Germany, M.S. Candidate, Interested in Distributed System, Iterative Processing Dept. of Computer Science, Informatik in German, TUB Technical University of Berlin In Korea, M.S. Candidate, Computer Architecture Laboratory Dept. of Computer Science, KAIST Rm# 4414 CS Dept. KAIST 373-1 Guseong-dong, Yuseong-gu, Daejon, South Korea (305-701) Mobile) 49) 015-251-448-278 in Germany, no cellular in Korea ==========================================================
