src/backend/nodes/README
Node Structures
===============
Andrew Yu (11/94)
Introduction
------------
The current node structures are plain old C structures. "Inheritance" is
achieved by convention. No additional functions will be generated. Functions
that manipulate node structures reside in this directory.
FILES IN THIS DIRECTORY (src/backend/nodes/)
General-purpose node manipulation functions:
copyfuncs.c - copy a node tree
equalfuncs.c - compare two node trees
outfuncs.c - convert a node tree to text representation
readfuncs.c - convert text representation back to a node tree
makefuncs.c - creator functions for some common node types
nodeFuncs.c - some other general-purpose manipulation functions
Specialized manipulation functions:
bitmapset.c - Bitmapset support
list.c - generic list support
params.c - Param support
tidbitmap.c - TIDBitmap support
value.c - support for Value nodes
FILES IN src/include/nodes/
Node definitions:
nodes.h - define node tags (NodeTag)
primnodes.h - primitive nodes
parsenodes.h - parse tree nodes
plannodes.h - plan tree nodes
relation.h - planner internal nodes
execnodes.h - executor nodes
memnodes.h - memory nodes
pg_list.h - generic list
Steps to Add a Node
-------------------
Suppose you wanna define a node Foo:
1. Add a tag (T_Foo) to the enum NodeTag in nodes.h. (If you insert the
tag in a way that moves the numbers associated with existing tags,
you'll need to recompile the whole tree after doing this. It doesn't
force initdb though, because the numbers never go to disk.)
2. Add the structure definition to the appropriate include/nodes/???.h file.
If you intend to inherit from, say a Plan node, put Plan as the first field
of your struct definition.
3. If you intend to use copyObject, equal, nodeToString or stringToNode,
add an appropriate function to copyfuncs.c, equalfuncs.c, outfuncs.c
and readfuncs.c accordingly. (Except for frequently used nodes, don't
bother writing a creator function in makefuncs.c) The header comments
in those files give general rules for whether you need to add support.
4. Add cases to the functions in nodeFuncs.c as needed. There are many
other places you'll probably also need to teach about your new node
type. Best bet is to grep for references to one or two similar existing
node types to find all the places to touch.
Historical Note
---------------
Prior to the current simple C structure definitions, the Node structures
used a pseudo-inheritance system which automatically generated creator and
accessor functions. Since every node inherited from LispValue, the whole thing
was a mess. Here's a little anecdote:
LispValue definition -- class used to support lisp structures
in C. This is here because we did not want to totally rewrite
planner and executor code which depended on lisp structures when
we ported postgres V1 from lisp to C. -cim 4/23/90
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Tom Lane
authored
This patch adds the ability to write TABLE( function1(), function2(), ...) as a single FROM-clause entry. The result is the concatenation of the first row from each function, followed by the second row from each function, etc; with NULLs inserted if any function produces fewer rows than others. This is believed to be a much more useful behavior than what Postgres currently does with multiple SRFs in a SELECT list. This syntax also provides a reasonable way to combine use of column definition lists with WITH ORDINALITY: put the column definition list inside TABLE(), where it's clear that it doesn't control the ordinality column as well. Also implement SQL-compliant multiple-argument UNNEST(), by turning UNNEST(a,b,c) into TABLE(unnest(a), unnest(b), unnest(c)). The SQL standard specifies TABLE() with only a single function, not multiple functions, and it seems to require an implicit UNNEST() which is not what this patch does. There may be something wrong with that reading of the spec, though, because if it's right then the spec's TABLE() is just a pointless alternative spelling of UNNEST(). After further review of that, we might choose to adopt a different syntax for what this patch does, but in any case this functionality seems clearly worthwhile. Andrew Gierth, reviewed by Zoltán Böszörményi and Heikki Linnakangas, and significantly revised by me
| Name | Last commit | Last update |
|---|---|---|
| .. | ||
| Makefile | ||
| README | ||
| bitmapset.c | ||
| copyfuncs.c | ||
| equalfuncs.c | ||
| list.c | ||
| makefuncs.c | ||
| nodeFuncs.c | ||
| nodes.c | ||
| outfuncs.c | ||
| params.c | ||
| print.c | ||
| read.c | ||
| readfuncs.c | ||
| tidbitmap.c | ||
| value.c | ||