Many thanks Phil for complementary information . Le sam. 24 mars 2018 à 09:53, HORDER Phil <phil.hor...@uk.thalesgroup.com> a écrit :
> Some databases will create a unique index for you when you create a > primary key. > > Oracle will create one, but only if you haven’t already done that. > > > > Postgres will ALWAYS create a unique index based on the primary key – so > you should never do that as well, or the db will have to maintain two > identical indexes. > > > > (When we migrated our db design from Oracle we ended up with lots of > duplicate indexes). > > > > SQL> Select * from pg_indexes order by schemaname, tablename; > > > > Phil Horder > > Database Mechanic > > > > Thales > > Land and Air Systems > > Horizon House, Throop Road, Templecombe, Somerset, BA8 0DH, UK > > www.thalesgroup.com/uk > > > > Tel: +44 (0) 1963 37 2041 > > Email: phil.hor...@uk.thalesgroup.com > > > > *Please consider the environment before printing a hard copy of this > email.* > > > > The information contained in this e-mail is confidential. It is intended > only for the stated addressee(s) and access to it by any other person is > unauthorised. If you are not an addressee, you must not disclose, copy, > circulate or in any other way use or rely on the information contained in > this e-mail. Such unauthorised use may be unlawful. If you have received > this e-mail in error, please inform us immediately on +44 (0)1963 370511 > and delete it and all copies from your system. > > > > *Thales UK Limited. A company registered in England and Wales. Registered > Office: 350 Longwater Avenue, Green Park, Reading, RG2 6GF. Registered > Number: 868273* > > > > *From:* Thomas Poty [mailto:thomas.p...@gmail.com] > *Sent:* 23 March 2018 07:56 > *To:* pgsql-general@lists.postgresql.org > *Subject:* primary key and unique index > > > > Hi all, > > I am migrating fromMySQL to Postgresql 9.6. > > In MySQL a "show create table" gives me : > ... > PRIMARY KEY (`ID`,`CountryCode`,`LanguageCode`), > UNIQUE KEY `unique_my table_4` (`ID`,`CountryCode`,`LanguageCode`), > ... > > So, In PostgreSQL, does it make sense to create a primary key AND a unique > index based on the same columns? > > Is PostgreSQL smart enough to use the unique index created for the primary > key. > > I know PostgreSQL can be based on a unique index to create a primary key > but I also know it is possible to create several indexes on the same > columns with the same order. > > Thanks > > Thomas >
