>> 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/