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) 1996-2017, 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 31051 : ExecResult(PlanState *pstate)
69 : {
70 31051 : ResultState *node = castNode(ResultState, pstate);
71 : TupleTableSlot *outerTupleSlot;
72 : PlanState *outerPlan;
73 : ExprContext *econtext;
74 :
75 31051 : CHECK_FOR_INTERRUPTS();
76 :
77 31051 : econtext = node->ps.ps_ExprContext;
78 :
79 : /*
80 : * check constant qualifications like (2 > 1), if not already done
81 : */
82 31051 : if (node->rs_checkqual)
83 : {
84 969 : bool qualResult = ExecQual(node->resconstantqual, econtext);
85 :
86 969 : node->rs_checkqual = false;
87 969 : if (!qualResult)
88 : {
89 772 : node->rs_done = true;
90 772 : 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 30279 : 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 30279 : while (!node->rs_done)
107 : {
108 22660 : outerPlan = outerPlanState(node);
109 :
110 22660 : if (outerPlan != NULL)
111 : {
112 : /*
113 : * retrieve tuples from the outer plan until there are no more.
114 : */
115 11086 : outerTupleSlot = ExecProcNode(outerPlan);
116 :
117 11086 : if (TupIsNull(outerTupleSlot))
118 256 : return NULL;
119 :
120 : /*
121 : * prepare to compute projection expressions, which will expect to
122 : * access the input tuples as varno OUTER.
123 : */
124 10830 : 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 11574 : node->rs_done = true;
133 : }
134 :
135 : /* form the result tuple using ExecProject(), and return it */
136 22404 : return ExecProject(node->ps.ps_ProjInfo);
137 : }
138 :
139 7619 : return NULL;
140 : }
141 :
142 : /* ----------------------------------------------------------------
143 : * ExecResultMarkPos
144 : * ----------------------------------------------------------------
145 : */
146 : void
147 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 11841 : ExecInitResult(Result *node, EState *estate, int eflags)
182 : {
183 : ResultState *resstate;
184 :
185 : /* check for unsupported flags */
186 11841 : Assert(!(eflags & (EXEC_FLAG_MARK | EXEC_FLAG_BACKWARD)) ||
187 : outerPlan(node) != NULL);
188 :
189 : /*
190 : * create state structure
191 : */
192 11841 : resstate = makeNode(ResultState);
193 11841 : resstate->ps.plan = (Plan *) node;
194 11841 : resstate->ps.state = estate;
195 11841 : resstate->ps.ExecProcNode = ExecResult;
196 :
197 11841 : resstate->rs_done = false;
198 11841 : resstate->rs_checkqual = (node->resconstantqual == NULL) ? false : true;
199 :
200 : /*
201 : * Miscellaneous initialization
202 : *
203 : * create expression context for node
204 : */
205 11841 : ExecAssignExprContext(estate, &resstate->ps);
206 :
207 : /*
208 : * tuple table initialization
209 : */
210 11841 : ExecInitResultTupleSlot(estate, &resstate->ps);
211 :
212 : /*
213 : * initialize child expressions
214 : */
215 11841 : resstate->ps.qual =
216 11841 : ExecInitQual(node->plan.qual, (PlanState *) resstate);
217 11841 : resstate->resconstantqual =
218 11841 : ExecInitQual((List *) node->resconstantqual, (PlanState *) resstate);
219 :
220 : /*
221 : * initialize child nodes
222 : */
223 11841 : outerPlanState(resstate) = ExecInitNode(outerPlan(node), estate, eflags);
224 :
225 : /*
226 : * we don't use inner plan
227 : */
228 11841 : Assert(innerPlan(node) == NULL);
229 :
230 : /*
231 : * initialize tuple type and projection info
232 : */
233 11841 : ExecAssignResultTypeFromTL(&resstate->ps);
234 11841 : ExecAssignProjectionInfo(&resstate->ps, NULL);
235 :
236 11839 : return resstate;
237 : }
238 :
239 : /* ----------------------------------------------------------------
240 : * ExecEndResult
241 : *
242 : * frees up storage allocated through C routines
243 : * ----------------------------------------------------------------
244 : */
245 : void
246 8831 : ExecEndResult(ResultState *node)
247 : {
248 : /*
249 : * Free the exprcontext
250 : */
251 8831 : ExecFreeExprContext(&node->ps);
252 :
253 : /*
254 : * clean out the tuple table
255 : */
256 8831 : ExecClearTuple(node->ps.ps_ResultTupleSlot);
257 :
258 : /*
259 : * shut down subplans
260 : */
261 8831 : ExecEndNode(outerPlanState(node));
262 8831 : }
263 :
264 : void
265 1249 : ExecReScanResult(ResultState *node)
266 : {
267 1249 : node->rs_done = false;
268 1249 : node->rs_checkqual = (node->resconstantqual == NULL) ? false : true;
269 :
270 : /*
271 : * If chgParam of subnode is not null then plan will be re-scanned by
272 : * first ExecProcNode.
273 : */
274 1935 : if (node->ps.lefttree &&
275 686 : node->ps.lefttree->chgParam == NULL)
276 12 : ExecReScan(node->ps.lefttree);
277 1249 : }
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