TLA Line data Source code
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) 1996-2023, 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 : #include "utils/memutils.h"
52 :
53 :
54 : /* ----------------------------------------------------------------
55 : * ExecResult(node)
56 : *
57 : * returns the tuples from the outer plan which satisfy the
58 : * qualification clause. Since result nodes with right
59 : * subtrees are never planned, we ignore the right subtree
60 : * entirely (for now).. -cim 10/7/89
61 : *
62 : * The qualification containing only constant clauses are
63 : * checked first before any processing is done. It always returns
64 : * 'nil' if the constant qualification is not satisfied.
65 : * ----------------------------------------------------------------
66 : */
67 : static TupleTableSlot *
68 CBC 675044 : ExecResult(PlanState *pstate)
69 : {
70 675044 : ResultState *node = castNode(ResultState, pstate);
71 : TupleTableSlot *outerTupleSlot;
72 : PlanState *outerPlan;
73 : ExprContext *econtext;
74 :
75 675044 : CHECK_FOR_INTERRUPTS();
76 :
77 675042 : econtext = node->ps.ps_ExprContext;
78 :
79 : /*
80 : * check constant qualifications like (2 > 1), if not already done
81 : */
82 675042 : if (node->rs_checkqual)
83 : {
84 6381 : bool qualResult = ExecQual(node->resconstantqual, econtext);
85 :
86 6381 : node->rs_checkqual = false;
87 6381 : if (!qualResult)
88 : {
89 3977 : node->rs_done = true;
90 3977 : return NULL;
91 : }
92 : }
93 :
94 : /*
95 : * Reset per-tuple memory context to free any expression evaluation
96 : * storage allocated in the previous tuple cycle.
97 : */
98 671065 : ResetExprContext(econtext);
99 :
100 : /*
101 : * if rs_done is true then it means that we were asked to return a
102 : * constant tuple and we already did the last time ExecResult() was
103 : * called, OR that we failed the constant qual check. Either way, now we
104 : * are through.
105 : */
106 671065 : if (!node->rs_done)
107 : {
108 485901 : outerPlan = outerPlanState(node);
109 :
110 485901 : if (outerPlan != NULL)
111 : {
112 : /*
113 : * retrieve tuples from the outer plan until there are no more.
114 : */
115 265370 : outerTupleSlot = ExecProcNode(outerPlan);
116 :
117 265363 : if (TupIsNull(outerTupleSlot))
118 3020 : return NULL;
119 :
120 : /*
121 : * prepare to compute projection expressions, which will expect to
122 : * access the input tuples as varno OUTER.
123 : */
124 262343 : econtext->ecxt_outertuple = outerTupleSlot;
125 : }
126 : else
127 : {
128 : /*
129 : * if we don't have an outer plan, then we are just generating the
130 : * results from a constant target list. Do it only once.
131 : */
132 220531 : node->rs_done = true;
133 : }
134 :
135 : /* form the result tuple using ExecProject(), and return it */
136 482874 : return ExecProject(node->ps.ps_ProjInfo);
137 : }
138 :
139 185164 : return NULL;
140 : }
141 :
142 : /* ----------------------------------------------------------------
143 : * ExecResultMarkPos
144 : * ----------------------------------------------------------------
145 : */
146 : void
147 UBC 0 : ExecResultMarkPos(ResultState *node)
148 : {
149 0 : PlanState *outerPlan = outerPlanState(node);
150 :
151 0 : if (outerPlan != NULL)
152 0 : ExecMarkPos(outerPlan);
153 : else
154 0 : elog(DEBUG2, "Result nodes do not support mark/restore");
155 0 : }
156 :
157 : /* ----------------------------------------------------------------
158 : * ExecResultRestrPos
159 : * ----------------------------------------------------------------
160 : */
161 : void
162 0 : ExecResultRestrPos(ResultState *node)
163 : {
164 0 : PlanState *outerPlan = outerPlanState(node);
165 :
166 0 : if (outerPlan != NULL)
167 0 : ExecRestrPos(outerPlan);
168 : else
169 0 : elog(ERROR, "Result nodes do not support mark/restore");
170 0 : }
171 :
172 : /* ----------------------------------------------------------------
173 : * ExecInitResult
174 : *
175 : * Creates the run-time state information for the result node
176 : * produced by the planner and initializes outer relations
177 : * (child nodes).
178 : * ----------------------------------------------------------------
179 : */
180 : ResultState *
181 CBC 147688 : ExecInitResult(Result *node, EState *estate, int eflags)
182 : {
183 : ResultState *resstate;
184 :
185 : /* check for unsupported flags */
186 147688 : Assert(!(eflags & (EXEC_FLAG_MARK | EXEC_FLAG_BACKWARD)) ||
187 : outerPlan(node) != NULL);
188 :
189 : /*
190 : * create state structure
191 : */
192 147688 : resstate = makeNode(ResultState);
193 147688 : resstate->ps.plan = (Plan *) node;
194 147688 : resstate->ps.state = estate;
195 147688 : resstate->ps.ExecProcNode = ExecResult;
196 :
197 147688 : resstate->rs_done = false;
198 147688 : resstate->rs_checkqual = (node->resconstantqual != NULL);
199 :
200 : /*
201 : * Miscellaneous initialization
202 : *
203 : * create expression context for node
204 : */
205 147688 : ExecAssignExprContext(estate, &resstate->ps);
206 :
207 : /*
208 : * initialize child nodes
209 : */
210 147688 : outerPlanState(resstate) = ExecInitNode(outerPlan(node), estate, eflags);
211 :
212 : /*
213 : * we don't use inner plan
214 : */
215 147688 : Assert(innerPlan(node) == NULL);
216 :
217 : /*
218 : * Initialize result slot, type and projection.
219 : */
220 147688 : ExecInitResultTupleSlotTL(&resstate->ps, &TTSOpsVirtual);
221 147688 : ExecAssignProjectionInfo(&resstate->ps, NULL);
222 :
223 : /*
224 : * initialize child expressions
225 : */
226 147653 : resstate->ps.qual =
227 147653 : ExecInitQual(node->plan.qual, (PlanState *) resstate);
228 147653 : resstate->resconstantqual =
229 147653 : ExecInitQual((List *) node->resconstantqual, (PlanState *) resstate);
230 :
231 147653 : return resstate;
232 : }
233 :
234 : /* ----------------------------------------------------------------
235 : * ExecEndResult
236 : *
237 : * frees up storage allocated through C routines
238 : * ----------------------------------------------------------------
239 : */
240 : void
241 139971 : ExecEndResult(ResultState *node)
242 : {
243 : /*
244 : * Free the exprcontext
245 : */
246 139971 : ExecFreeExprContext(&node->ps);
247 :
248 : /*
249 : * clean out the tuple table
250 : */
251 139971 : ExecClearTuple(node->ps.ps_ResultTupleSlot);
252 :
253 : /*
254 : * shut down subplans
255 : */
256 139971 : ExecEndNode(outerPlanState(node));
257 139971 : }
258 :
259 : void
260 83622 : ExecReScanResult(ResultState *node)
261 : {
262 GNC 83622 : PlanState *outerPlan = outerPlanState(node);
263 :
264 CBC 83622 : node->rs_done = false;
265 GIC 83622 : node->rs_checkqual = (node->resconstantqual != NULL);
266 ECB :
267 : /*
268 : * If chgParam of subnode is not null then plan will be re-scanned by
269 : * first ExecProcNode.
270 : */
271 GNC 83622 : if (outerPlan && outerPlan->chgParam == NULL)
272 39 : ExecReScan(outerPlan);
273 CBC 83622 : }
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