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体验新版 GitCode,发现更多精彩内容 >>
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148ec3b1
编写于
2月 20, 1999
作者:
B
Bruce Momjian
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update pathkey description.
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src/backend/optimizer/path/pathkeys.c
src/backend/optimizer/path/pathkeys.c
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src/backend/optimizer/path/pathkeys.c
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148ec3b1
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@@ -7,7 +7,7 @@
*
*
* 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 $
*
*-------------------------------------------------------------------------
*/
...
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@@ -38,7 +38,7 @@ static List *new_matching_subkeys(Var *subkey, List *considered_subkeys,
/*
* 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.
*
* In single/base relation RelOptInfo's, the Path's represent various ways
...
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@@ -49,8 +49,8 @@ static List *new_matching_subkeys(Var *subkey, List *considered_subkeys,
*
* Multi-relation RelOptInfo Path's are more complicated. Mergejoins are
* only performed with equajoins("="). Because of this, the multi-relation
* path actually has more than one
ordering. For example, a mergejoin Path
* of "tab1.col1 = tab2.col1" would generate a pathkeys of
* path actually has more than one
primary Var key. For example, a
*
mergejoin Path
of "tab1.col1 = tab2.col1" would generate a pathkeys of
* { {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.
* They are equal, so they are both primary sort keys. This is why pathkeys
...
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