PostgreSQL Source Code: src/backend/executor/nodeResult.c Source File

PostgreSQL Source Code git master
nodeResult.c
Go to the documentation of this file.
1/*-------------------------------------------------------------------------
2 *
3 * nodeResult.c
4 * support for constant nodes needing special code.
5 *
6 * DESCRIPTION
7 *
8 * Result nodes are used in queries where no relations are scanned.
9 * Examples of such queries are:
10 *
11 * select 1 * 2
12 *
13 * insert into emp values ('mike', 15000)
14 *
15 * (Remember that in an INSERT or UPDATE, we need a plan tree that
16 * generates the new rows.)
17 *
18 * Result nodes are also used to optimise queries with constant
19 * qualifications (ie, quals that do not depend on the scanned data),
20 * such as:
21 *
22 * select * from emp where 2 > 1
23 *
24 * In this case, the plan generated is
25 *
26 * Result (with 2 > 1 qual)
27 * /
28 * SeqScan (emp.*)
29 *
30 * At runtime, the Result node evaluates the constant qual once,
31 * which is shown by EXPLAIN as a One-Time Filter. If it's
32 * false, we can return an empty result set without running the
33 * controlled plan at all. If it's true, we run the controlled
34 * plan normally and pass back the results.
35 *
36 *
37 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
38 * Portions Copyright (c) 1994, Regents of the University of California
39 *
40 * IDENTIFICATION
41 * src/backend/executor/nodeResult.c
42 *
43 *-------------------------------------------------------------------------
44 */
45
46#include "postgres.h"
47
48#include "executor/executor.h"
49#include "executor/nodeResult.h"
50#include "miscadmin.h"
51
52
53/* ----------------------------------------------------------------
54 * ExecResult(node)
55 *
56 * returns the tuples from the outer plan which satisfy the
57 * qualification clause. Since result nodes with right
58 * subtrees are never planned, we ignore the right subtree
59 * entirely (for now).. -cim 10/7/89
60 *
61 * The qualification containing only constant clauses are
62 * checked first before any processing is done. It always returns
63 * 'nil' if the constant qualification is not satisfied.
64 * ----------------------------------------------------------------
65 */
66static TupleTableSlot *
67 ExecResult(PlanState *pstate)
68{
69 ResultState *node = castNode(ResultState, pstate);
70 TupleTableSlot *outerTupleSlot;
71 PlanState *outerPlan;
72 ExprContext *econtext;
73
74 CHECK_FOR_INTERRUPTS();
75
76 econtext = node->ps.ps_ExprContext;
77
78 /*
79 * check constant qualifications like (2 > 1), if not already done
80 */
81 if (node->rs_checkqual)
82 {
83 bool qualResult = ExecQual(node->resconstantqual, econtext);
84
85 node->rs_checkqual = false;
86 if (!qualResult)
87 {
88 node->rs_done = true;
89 return NULL;
90 }
91 }
92
93 /*
94 * Reset per-tuple memory context to free any expression evaluation
95 * storage allocated in the previous tuple cycle.
96 */
97 ResetExprContext(econtext);
98
99 /*
100 * if rs_done is true then it means that we were asked to return a
101 * constant tuple and we already did the last time ExecResult() was
102 * called, OR that we failed the constant qual check. Either way, now we
103 * are through.
104 */
105 if (!node->rs_done)
106 {
107 outerPlan = outerPlanState(node);
108
109 if (outerPlan != NULL)
110 {
111 /*
112 * retrieve tuples from the outer plan until there are no more.
113 */
114 outerTupleSlot = ExecProcNode(outerPlan);
115
116 if (TupIsNull(outerTupleSlot))
117 return NULL;
118
119 /*
120 * prepare to compute projection expressions, which will expect to
121 * access the input tuples as varno OUTER.
122 */
123 econtext->ecxt_outertuple = outerTupleSlot;
124 }
125 else
126 {
127 /*
128 * if we don't have an outer plan, then we are just generating the
129 * results from a constant target list. Do it only once.
130 */
131 node->rs_done = true;
132 }
133
134 /* form the result tuple using ExecProject(), and return it */
135 return ExecProject(node->ps.ps_ProjInfo);
136 }
137
138 return NULL;
139}
140
141/* ----------------------------------------------------------------
142 * ExecResultMarkPos
143 * ----------------------------------------------------------------
144 */
145void
146 ExecResultMarkPos(ResultState *node)
147{
148 PlanState *outerPlan = outerPlanState(node);
149
150 if (outerPlan != NULL)
151 ExecMarkPos(outerPlan);
152 else
153 elog(DEBUG2, "Result nodes do not support mark/restore");
154}
155
156/* ----------------------------------------------------------------
157 * ExecResultRestrPos
158 * ----------------------------------------------------------------
159 */
160void
161 ExecResultRestrPos(ResultState *node)
162{
163 PlanState *outerPlan = outerPlanState(node);
164
165 if (outerPlan != NULL)
166 ExecRestrPos(outerPlan);
167 else
168 elog(ERROR, "Result nodes do not support mark/restore");
169}
170
171/* ----------------------------------------------------------------
172 * ExecInitResult
173 *
174 * Creates the run-time state information for the result node
175 * produced by the planner and initializes outer relations
176 * (child nodes).
177 * ----------------------------------------------------------------
178 */
179ResultState *
180 ExecInitResult(Result *node, EState *estate, int eflags)
181{
182 ResultState *resstate;
183
184 /* check for unsupported flags */
185 Assert(!(eflags & (EXEC_FLAG_MARK | EXEC_FLAG_BACKWARD)) ||
186 outerPlan(node) != NULL);
187
188 /*
189 * create state structure
190 */
191 resstate = makeNode(ResultState);
192 resstate->ps.plan = (Plan *) node;
193 resstate->ps.state = estate;
194 resstate->ps.ExecProcNode = ExecResult;
195
196 resstate->rs_done = false;
197 resstate->rs_checkqual = (node->resconstantqual != NULL);
198
199 /*
200 * Miscellaneous initialization
201 *
202 * create expression context for node
203 */
204 ExecAssignExprContext(estate, &resstate->ps);
205
206 /*
207 * initialize child nodes
208 */
209 outerPlanState(resstate) = ExecInitNode(outerPlan(node), estate, eflags);
210
211 /*
212 * we don't use inner plan
213 */
214 Assert(innerPlan(node) == NULL);
215
216 /*
217 * Initialize result slot, type and projection.
218 */
219 ExecInitResultTupleSlotTL(&resstate->ps, &TTSOpsVirtual);
220 ExecAssignProjectionInfo(&resstate->ps, NULL);
221
222 /*
223 * initialize child expressions
224 */
225 resstate->ps.qual =
226 ExecInitQual(node->plan.qual, (PlanState *) resstate);
227 resstate->resconstantqual =
228 ExecInitQual((List *) node->resconstantqual, (PlanState *) resstate);
229
230 return resstate;
231}
232
233/* ----------------------------------------------------------------
234 * ExecEndResult
235 *
236 * frees up storage allocated through C routines
237 * ----------------------------------------------------------------
238 */
239void
240 ExecEndResult(ResultState *node)
241{
242 /*
243 * shut down subplans
244 */
245 ExecEndNode(outerPlanState(node));
246}
247
248void
249 ExecReScanResult(ResultState *node)
250{
251 PlanState *outerPlan = outerPlanState(node);
252
253 node->rs_done = false;
254 node->rs_checkqual = (node->resconstantqual != NULL);
255
256 /*
257 * If chgParam of subnode is not null then plan will be re-scanned by
258 * first ExecProcNode.
259 */
260 if (outerPlan && outerPlan->chgParam == NULL)
261 ExecReScan(outerPlan);
262}
#define DEBUG2
Definition: elog.h:29
#define ERROR
Definition: elog.h:39
#define elog(elevel,...)
Definition: elog.h:226
void ExecMarkPos(PlanState *node)
Definition: execAmi.c:327
void ExecReScan(PlanState *node)
Definition: execAmi.c:77
void ExecRestrPos(PlanState *node)
Definition: execAmi.c:376
ExprState * ExecInitQual(List *qual, PlanState *parent)
Definition: execExpr.c:229
void ExecEndNode(PlanState *node)
Definition: execProcnode.c:562
PlanState * ExecInitNode(Plan *node, EState *estate, int eflags)
Definition: execProcnode.c:142
const TupleTableSlotOps TTSOpsVirtual
Definition: execTuples.c:84
void ExecInitResultTupleSlotTL(PlanState *planstate, const TupleTableSlotOps *tts_ops)
Definition: execTuples.c:1988
void ExecAssignExprContext(EState *estate, PlanState *planstate)
Definition: execUtils.c:485
void ExecAssignProjectionInfo(PlanState *planstate, TupleDesc inputDesc)
Definition: execUtils.c:583
#define outerPlanState(node)
Definition: execnodes.h:1255
#define EXEC_FLAG_BACKWARD
Definition: executor.h:69
static TupleTableSlot * ExecProject(ProjectionInfo *projInfo)
Definition: executor.h:480
#define ResetExprContext(econtext)
Definition: executor.h:647
static bool ExecQual(ExprState *state, ExprContext *econtext)
Definition: executor.h:516
static TupleTableSlot * ExecProcNode(PlanState *node)
Definition: executor.h:311
#define EXEC_FLAG_MARK
Definition: executor.h:70
Assert(PointerIsAligned(start, uint64))
#define CHECK_FOR_INTERRUPTS()
Definition: miscadmin.h:122
void ExecReScanResult(ResultState *node)
Definition: nodeResult.c:249
static TupleTableSlot * ExecResult(PlanState *pstate)
Definition: nodeResult.c:67
ResultState * ExecInitResult(Result *node, EState *estate, int eflags)
Definition: nodeResult.c:180
void ExecEndResult(ResultState *node)
Definition: nodeResult.c:240
void ExecResultRestrPos(ResultState *node)
Definition: nodeResult.c:161
void ExecResultMarkPos(ResultState *node)
Definition: nodeResult.c:146
#define makeNode(_type_)
Definition: nodes.h:161
#define castNode(_type_, nodeptr)
Definition: nodes.h:182
#define innerPlan(node)
Definition: plannodes.h:251
#define outerPlan(node)
Definition: plannodes.h:252
Definition: execnodes.h:655
TupleTableSlot * ecxt_outertuple
Definition: execnodes.h:277
Definition: pg_list.h:54
ExprState * qual
Definition: execnodes.h:1180
Plan * plan
Definition: execnodes.h:1159
EState * state
Definition: execnodes.h:1161
ExprContext * ps_ExprContext
Definition: execnodes.h:1198
ProjectionInfo * ps_ProjInfo
Definition: execnodes.h:1199
ExecProcNodeMtd ExecProcNode
Definition: execnodes.h:1165
Definition: plannodes.h:177
List * qual
Definition: plannodes.h:222
ExprState * resconstantqual
Definition: execnodes.h:1363
bool rs_done
Definition: execnodes.h:1364
PlanState ps
Definition: execnodes.h:1362
bool rs_checkqual
Definition: execnodes.h:1365
Definition: plannodes.h:287
Node * resconstantqual
Definition: plannodes.h:290
Plan plan
Definition: plannodes.h:288
#define TupIsNull(slot)
Definition: tuptable.h:309

AltStyle によって変換されたページ (->オリジナル) /