$PostgreSQL: pgsql/src/backend/nodes/README,v 1.3 2008/03/20 17:55:14 momjian Exp $ 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 Node manipulation functions: copyfuncs.c - copying a node equalfuncs.c - comparing a node outfuncs.c - convert a node to ascii representation readfuncs.c - convert ascii representation back to a node makefuncs.c - creator functions for primitive nodes Node definitions: nodes.h - define node tags (NodeTag) pg_list.h - generic list primnodes.h - primitive nodes parsenodes.h - parse tree nodes plannodes.h - plan tree nodes relation.h - inner plan tree nodes execnodes.h - executor nodes memnodes.h - memory nodes Steps to Add a Node ------------------- Suppose you wana define a node Foo: 1. add a tag (T_Foo) to the enum NodeTag in nodes.h (You may have to recompile the whole tree after doing this.) 2. add the structure definition to the appropriate ???nodes.h file. If you intend to inherit from, say a Plan node, put Plan as the first field of you 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) Historical Note --------------- Prior to the current simple C structure definitions, the Node structures uses a pseudo-inheritance system which automatically generates creator and accessor functions. Since every node inherits from LispValue, the whole thing is 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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but seem like a separate patch since most of the remaining work is on the executor side.) I took the opportunity to push selection of the grouping operators for set operations into the parser where it belongs. Otherwise this is just a small exercise in making prepunion.c consider both alternatives. As with the recent DISTINCT patch, this means we can UNION on datatypes that can hash but not sort, and it means that UNION without ORDER BY is no longer certain to produce sorted output.
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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 |