Message-ID: <55F70D0A.2030503@sigaev.ru>
Date: Mon, 14 Sep 2015 21:08:10 +0300
From: Teodor Sigaev <teodor@sigaev.ru>
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To: Jim Nasby <Jim.Nasby@BlueTreble.com>,
 Anastasia Lubennikova <a.lubennikova@postgrespro.ru>,
 pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: [PROPOSAL] Covering + unique indexes.
References: <55F2C1BC.3010109@postgrespro.ru>
 <55F2CCD0.7040608@postgrespro.ru> <55F6F7AD.4080307@BlueTreble.com>
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>> CREATE INDEX index ON table (c1, c2, c3) UNIQUE ON (c1, c3);
>>
>> CREATE [UNIQUE {ON FIRST {COLUMN | n_unique_column COLUMNS}} INDEX ON
>> table_name (column_name1, column_name2 ...);
>
> I would use the first (simple) syntax and just throw an error if the
> user tries to skip a column on the UNIQUE clause.
Seems, second option looks as more natural extension of CREATE UNIQUE INDEX


>
> Have you by chance looked to see what other databases have done for
> syntax? I'm guessing this isn't covered by ANSI but maybe there's
> already an industry consensus.

MS SQL and DB/2 suggests (with changes for postgresql):
CREATE UNIQUE INDEX i ON t (a,b) INCLUDE (c)

MS SQL supports both unique and non-unique indexes, DB/2 only unique 
indexes. Oracle/MySQL doesn't support covering indexes. Readed at 
http://use-the-index-luke.com/sql/clustering/index-only-scan-covering-index


MSSQL/DB/2 variants looks good too.

-- 
Teodor Sigaev                      E-mail: teodor@sigaev.ru
                                       WWW: http://www.sigaev.ru/


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