From: | Teodor Sigaev <teodor(at)sigaev(dot)ru> |
---|---|
To: | Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com>, Anastasia Lubennikova <a(dot)lubennikova(at)postgrespro(dot)ru>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [PROPOSAL] Covering + unique indexes. |
Date: | 2015-09-14 18:08:10 |
Message-ID: | 55F70D0A.2030503@sigaev.ru |
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Lists: | pgsql-hackers |
>> 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(at)sigaev(dot)ru
WWW: http://www.sigaev.ru/
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