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update pathkey description.

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This commit is contained in:
Bruce Momjian 1999-02-20 16:32:35 +00:00
parent 9188aab758
commit 148ec3b1d8
1 changed files with 4 additions and 4 deletions
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8
src/backend/optimizer/path/pathkeys.c
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@ -7,7 +7,7 @@
* *
* *
* IDENTIFICATION * IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/pathkeys.c,v 1.2 1999/02/20 16:28:20 momjian Exp $ * $Header: /cvsroot/pgsql/src/backend/optimizer/path/pathkeys.c,v 1.3 1999/02/20 16:32:35 momjian Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -38,7 +38,7 @@ static List *new_matching_subkeys(Var *subkey, List *considered_subkeys,
/* /*
* Explanation of Path.pathkeys * Explanation of Path.pathkeys
* *
* This structure is a List of List of Var nodes that represent the sort * Path.pathkeys is a List of List of Var nodes that represent the sort
* order of the result generated by the Path. * order of the result generated by the Path.
* *
* In single/base relation RelOptInfo's, the Path's represent various ways * In single/base relation RelOptInfo's, the Path's represent various ways
@ -49,8 +49,8 @@ static List *new_matching_subkeys(Var *subkey, List *considered_subkeys,
* *
* Multi-relation RelOptInfo Path's are more complicated. Mergejoins are * Multi-relation RelOptInfo Path's are more complicated. Mergejoins are
* only performed with equajoins("="). Because of this, the multi-relation * only performed with equajoins("="). Because of this, the multi-relation
* path actually has more than one ordering. For example, a mergejoin Path * path actually has more than one primary Var key. For example, a
* of "tab1.col1 = tab2.col1" would generate a pathkeys of * mergejoin Path of "tab1.col1 = tab2.col1" would generate a pathkeys of
* { {tab1.col1, tab2.col1} }. This allows future joins to use either Var * { {tab1.col1, tab2.col1} }. This allows future joins to use either Var
* as a pre-sorted key to prevent Mergejoins from having to re-sort the Path. * as a pre-sorted key to prevent Mergejoins from having to re-sort the Path.
* They are equal, so they are both primary sort keys. This is why pathkeys * They are equal, so they are both primary sort keys. This is why pathkeys