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: teo...@sigaev.ru
WWW: http://www.sigaev.ru/
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