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| author | Teodor Sigaev <teodor@sigaev.ru> | 2018-01-11 14:49:36 +0300 |
|---|---|---|
| committer | Teodor Sigaev <teodor@sigaev.ru> | 2018-01-11 14:49:36 +0300 |
| commit | f50c80dbb17efa39c169f6c510e9464486ff5edc (patch) | |
| tree | 28bd442434d2c59b6f2662e600440a4a30c4374a /doc/src | |
| parent | 563a053bdd4b91c5e5560f4bf91220e562326f7d (diff) | |
llow negative coordinate for ~> (cube, int) operator
~> (cube, int) operator was especially designed for knn-gist search.
However, knn-gist supports only ascending ordering of results. Nevertheless
it would be useful to support descending ordering by ~> (cube, int) operator.
We provide workaround for that: negative coordinate give us inversed value
of corresponding cube bound. Therefore, knn search using negative coordinate
gives us an effect of descending ordering by cube bound.
Author: Alexander Korotkov
Reviewed by: Tomas Vondra, Andrey Borodin
Discussion: https://www.postgresql.org/message-id/flat/a9657f6a-b497-36ff-e56-482a2c7e3292@2ndquadrant.com
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/cube.sgml | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/doc/src/sgml/cube.sgml b/doc/src/sgml/cube.sgml index 9cda8cac972..e010305d848 100644 --- a/doc/src/sgml/cube.sgml +++ b/doc/src/sgml/cube.sgml @@ -189,8 +189,9 @@ Get <replaceable>n</replaceable>-th coordinate of cube in following way: n = 2 * k - 1 means lower bound of <replaceable>k</replaceable>-th dimension, n = 2 * k means upper bound of - <replaceable>k</replaceable>-th dimension. This operator is designed - for KNN-GiST support. + <replaceable>k</replaceable>-th dimension. Negative + <replaceable>n</replaceable> denotes inversed value of corresponding + positive coordinate. This operator is designed for KNN-GiST support. </entry> </row> |