1 /*-------------------------------------------------------------------------
2 *
3 * view.c
4 * use rewrite rules to construct views
5 *
6 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
7 * Portions Copyright (c) 1994, Regents of the University of California
8 *
9 *
10 * IDENTIFICATION
11 * src/backend/commands/view.c
12 *
13 *-------------------------------------------------------------------------
14 */
15 #include "postgres.h"
16
17 #include "access/relation.h"
18 #include "access/xact.h"
19 #include "catalog/namespace.h"
20 #include "commands/defrem.h"
21 #include "commands/tablecmds.h"
22 #include "commands/view.h"
23 #include "miscadmin.h"
24 #include "nodes/makefuncs.h"
25 #include "nodes/nodeFuncs.h"
26 #include "parser/analyze.h"
27 #include "parser/parse_relation.h"
28 #include "rewrite/rewriteDefine.h"
29 #include "rewrite/rewriteHandler.h"
30 #include "rewrite/rewriteManip.h"
31 #include "rewrite/rewriteSupport.h"
32 #include "utils/acl.h"
33 #include "utils/builtins.h"
34 #include "utils/lsyscache.h"
35 #include "utils/rel.h"
36 #include "utils/syscache.h"
37
38 static void checkViewTupleDesc(TupleDesc newdesc, TupleDesc olddesc);
39
40 /*---------------------------------------------------------------------
41 * DefineVirtualRelation
42 *
43 * Create a view relation and use the rules system to store the query
44 * for the view.
45 *
46 * EventTriggerAlterTableStart must have been called already.
47 *---------------------------------------------------------------------
48 */
49 static ObjectAddress
DefineVirtualRelation(RangeVar * relation,List * tlist,bool replace,List * options,Query * viewParse)50 DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
51 List *options, Query *viewParse)
52 {
53 Oid viewOid;
54 LOCKMODE lockmode;
55 CreateStmt *createStmt = makeNode(CreateStmt);
56 List *attrList;
57 ListCell *t;
58
59 /*
60 * create a list of ColumnDef nodes based on the names and types of the
61 * (non-junk) targetlist items from the view's SELECT list.
62 */
63 attrList = NIL;
64 foreach(t, tlist)
65 {
66 TargetEntry *tle = (TargetEntry *) lfirst(t);
67
68 if (!tle->resjunk)
69 {
70 ColumnDef *def = makeColumnDef(tle->resname,
71 exprType((Node *) tle->expr),
72 exprTypmod((Node *) tle->expr),
73 exprCollation((Node *) tle->expr));
74
75 /*
76 * It's possible that the column is of a collatable type but the
77 * collation could not be resolved, so double-check.
78 */
79 if (type_is_collatable(exprType((Node *) tle->expr)))
80 {
81 if (!OidIsValid(def->collOid))
82 ereport(ERROR,
83 (errcode(ERRCODE_INDETERMINATE_COLLATION),
84 errmsg("could not determine which collation to use for view column \"%s\"",
85 def->colname),
86 errhint("Use the COLLATE clause to set the collation explicitly.")));
87 }
88 else
89 Assert(!OidIsValid(def->collOid));
90
91 attrList = lappend(attrList, def);
92 }
93 }
94
95 /*
96 * Look up, check permissions on, and lock the creation namespace; also
97 * check for a preexisting view with the same name. This will also set
98 * relation->relpersistence to RELPERSISTENCE_TEMP if the selected
99 * namespace is temporary.
100 */
101 lockmode = replace ? AccessExclusiveLock : NoLock;
102 (void) RangeVarGetAndCheckCreationNamespace(relation, lockmode, &viewOid);
103
104 if (OidIsValid(viewOid) && replace)
105 {
106 Relation rel;
107 TupleDesc descriptor;
108 List *atcmds = NIL;
109 AlterTableCmd *atcmd;
110 ObjectAddress address;
111
112 /* Relation is already locked, but we must build a relcache entry. */
113 rel = relation_open(viewOid, NoLock);
114
115 /* Make sure it *is* a view. */
116 if (rel->rd_rel->relkind != RELKIND_VIEW)
117 ereport(ERROR,
118 (errcode(ERRCODE_WRONG_OBJECT_TYPE),
119 errmsg("\"%s\" is not a view",
120 RelationGetRelationName(rel))));
121
122 /* Also check it's not in use already */
123 CheckTableNotInUse(rel, "CREATE OR REPLACE VIEW");
124
125 /*
126 * Due to the namespace visibility rules for temporary objects, we
127 * should only end up replacing a temporary view with another
128 * temporary view, and similarly for permanent views.
129 */
130 Assert(relation->relpersistence == rel->rd_rel->relpersistence);
131
132 /*
133 * Create a tuple descriptor to compare against the existing view, and
134 * verify that the old column list is an initial prefix of the new
135 * column list.
136 */
137 descriptor = BuildDescForRelation(attrList);
138 checkViewTupleDesc(descriptor, rel->rd_att);
139
140 /*
141 * If new attributes have been added, we must add pg_attribute entries
142 * for them. It is convenient (although overkill) to use the ALTER
143 * TABLE ADD COLUMN infrastructure for this.
144 *
145 * Note that we must do this before updating the query for the view,
146 * since the rules system requires that the correct view columns be in
147 * place when defining the new rules.
148 *
149 * Also note that ALTER TABLE doesn't run parse transformation on
150 * AT_AddColumnToView commands. The ColumnDef we supply must be ready
151 * to execute as-is.
152 */
153 if (list_length(attrList) > rel->rd_att->natts)
154 {
155 ListCell *c;
156 int skip = rel->rd_att->natts;
157
158 foreach(c, attrList)
159 {
160 if (skip > 0)
161 {
162 skip--;
163 continue;
164 }
165 atcmd = makeNode(AlterTableCmd);
166 atcmd->subtype = AT_AddColumnToView;
167 atcmd->def = (Node *) lfirst(c);
168 atcmds = lappend(atcmds, atcmd);
169 }
170
171 /* EventTriggerAlterTableStart called by ProcessUtilitySlow */
172 AlterTableInternal(viewOid, atcmds, true);
173
174 /* Make the new view columns visible */
175 CommandCounterIncrement();
176 }
177
178 /*
179 * Update the query for the view.
180 *
181 * Note that we must do this before updating the view options, because
182 * the new options may not be compatible with the old view query (for
183 * example if we attempt to add the WITH CHECK OPTION, we require that
184 * the new view be automatically updatable, but the old view may not
185 * have been).
186 */
187 StoreViewQuery(viewOid, viewParse, replace);
188
189 /* Make the new view query visible */
190 CommandCounterIncrement();
191
192 /*
193 * Finally update the view options.
194 *
195 * The new options list replaces the existing options list, even if
196 * it's empty.
197 */
198 atcmd = makeNode(AlterTableCmd);
199 atcmd->subtype = AT_ReplaceRelOptions;
200 atcmd->def = (Node *) options;
201 atcmds = list_make1(atcmd);
202
203 /* EventTriggerAlterTableStart called by ProcessUtilitySlow */
204 AlterTableInternal(viewOid, atcmds, true);
205
206 ObjectAddressSet(address, RelationRelationId, viewOid);
207
208 /*
209 * Seems okay, so return the OID of the pre-existing view.
210 */
211 relation_close(rel, NoLock); /* keep the lock! */
212
213 return address;
214 }
215 else
216 {
217 ObjectAddress address;
218
219 /*
220 * Set the parameters for keys/inheritance etc. All of these are
221 * uninteresting for views...
222 */
223 createStmt->relation = relation;
224 createStmt->tableElts = attrList;
225 createStmt->inhRelations = NIL;
226 createStmt->constraints = NIL;
227 createStmt->options = options;
228 createStmt->oncommit = ONCOMMIT_NOOP;
229 createStmt->tablespacename = NULL;
230 createStmt->if_not_exists = false;
231
232 /*
233 * Create the relation (this will error out if there's an existing
234 * view, so we don't need more code to complain if "replace" is
235 * false).
236 */
237 address = DefineRelation(createStmt, RELKIND_VIEW, InvalidOid, NULL,
238 NULL);
239 Assert(address.objectId != InvalidOid);
240
241 /* Make the new view relation visible */
242 CommandCounterIncrement();
243
244 /* Store the query for the view */
245 StoreViewQuery(address.objectId, viewParse, replace);
246
247 return address;
248 }
249 }
250
251 /*
252 * Verify that tupledesc associated with proposed new view definition
253 * matches tupledesc of old view. This is basically a cut-down version
254 * of equalTupleDescs(), with code added to generate specific complaints.
255 * Also, we allow the new tupledesc to have more columns than the old.
256 */
257 static void
checkViewTupleDesc(TupleDesc newdesc,TupleDesc olddesc)258 checkViewTupleDesc(TupleDesc newdesc, TupleDesc olddesc)
259 {
260 int i;
261
262 if (newdesc->natts < olddesc->natts)
263 ereport(ERROR,
264 (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
265 errmsg("cannot drop columns from view")));
266
267 for (i = 0; i < olddesc->natts; i++)
268 {
269 Form_pg_attribute newattr = TupleDescAttr(newdesc, i);
270 Form_pg_attribute oldattr = TupleDescAttr(olddesc, i);
271
272 /* XXX msg not right, but we don't support DROP COL on view anyway */
273 if (newattr->attisdropped != oldattr->attisdropped)
274 ereport(ERROR,
275 (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
276 errmsg("cannot drop columns from view")));
277
278 if (strcmp(NameStr(newattr->attname), NameStr(oldattr->attname)) != 0)
279 ereport(ERROR,
280 (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
281 errmsg("cannot change name of view column \"%s\" to \"%s\"",
282 NameStr(oldattr->attname),
283 NameStr(newattr->attname)),
284 errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
285 /* XXX would it be safe to allow atttypmod to change? Not sure */
286 if (newattr->atttypid != oldattr->atttypid ||
287 newattr->atttypmod != oldattr->atttypmod)
288 ereport(ERROR,
289 (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
290 errmsg("cannot change data type of view column \"%s\" from %s to %s",
291 NameStr(oldattr->attname),
292 format_type_with_typemod(oldattr->atttypid,
293 oldattr->atttypmod),
294 format_type_with_typemod(newattr->atttypid,
295 newattr->atttypmod))));
296 /* We can ignore the remaining attributes of an attribute... */
297 }
298
299 /*
300 * We ignore the constraint fields. The new view desc can't have any
301 * constraints, and the only ones that could be on the old view are
302 * defaults, which we are happy to leave in place.
303 */
304 }
305
306 static void
DefineViewRules(Oid viewOid,Query * viewParse,bool replace)307 DefineViewRules(Oid viewOid, Query *viewParse, bool replace)
308 {
309 /*
310 * Set up the ON SELECT rule. Since the query has already been through
311 * parse analysis, we use DefineQueryRewrite() directly.
312 */
313 DefineQueryRewrite(pstrdup(ViewSelectRuleName),
314 viewOid,
315 NULL,
316 CMD_SELECT,
317 true,
318 replace,
319 list_make1(viewParse));
320
321 /*
322 * Someday: automatic ON INSERT, etc
323 */
324 }
325
326 /*---------------------------------------------------------------
327 * UpdateRangeTableOfViewParse
328 *
329 * Update the range table of the given parsetree.
330 * This update consists of adding two new entries IN THE BEGINNING
331 * of the range table (otherwise the rule system will die a slow,
332 * horrible and painful death, and we do not want that now, do we?)
333 * one for the OLD relation and one for the NEW one (both of
334 * them refer in fact to the "view" relation).
335 *
336 * Of course we must also increase the 'varnos' of all the Var nodes
337 * by 2...
338 *
339 * These extra RT entries are not actually used in the query,
340 * except for run-time locking and permission checking.
341 *---------------------------------------------------------------
342 */
343 static Query *
UpdateRangeTableOfViewParse(Oid viewOid,Query * viewParse)344 UpdateRangeTableOfViewParse(Oid viewOid, Query *viewParse)
345 {
346 Relation viewRel;
347 List *new_rt;
348 ParseNamespaceItem *nsitem;
349 RangeTblEntry *rt_entry1,
350 *rt_entry2;
351 ParseState *pstate;
352
353 /*
354 * Make a copy of the given parsetree. It's not so much that we don't
355 * want to scribble on our input, it's that the parser has a bad habit of
356 * outputting multiple links to the same subtree for constructs like
357 * BETWEEN, and we mustn't have OffsetVarNodes increment the varno of a
358 * Var node twice. copyObject will expand any multiply-referenced subtree
359 * into multiple copies.
360 */
361 viewParse = copyObject(viewParse);
362
363 /* Create a dummy ParseState for addRangeTableEntryForRelation */
364 pstate = make_parsestate(NULL);
365
366 /* need to open the rel for addRangeTableEntryForRelation */
367 viewRel = relation_open(viewOid, AccessShareLock);
368
369 /*
370 * Create the 2 new range table entries and form the new range table...
371 * OLD first, then NEW....
372 */
373 nsitem = addRangeTableEntryForRelation(pstate, viewRel,
374 AccessShareLock,
375 makeAlias("old", NIL),
376 false, false);
377 rt_entry1 = nsitem->p_rte;
378 nsitem = addRangeTableEntryForRelation(pstate, viewRel,
379 AccessShareLock,
380 makeAlias("new", NIL),
381 false, false);
382 rt_entry2 = nsitem->p_rte;
383
384 /* Must override addRangeTableEntry's default access-check flags */
385 rt_entry1->requiredPerms = 0;
386 rt_entry2->requiredPerms = 0;
387
388 new_rt = lcons(rt_entry1, lcons(rt_entry2, viewParse->rtable));
389
390 viewParse->rtable = new_rt;
391
392 /*
393 * Now offset all var nodes by 2, and jointree RT indexes too.
394 */
395 OffsetVarNodes((Node *) viewParse, 2, 0);
396
397 relation_close(viewRel, AccessShareLock);
398
399 return viewParse;
400 }
401
402 /*
403 * DefineView
404 * Execute a CREATE VIEW command.
405 */
406 ObjectAddress
DefineView(ViewStmt * stmt,const char * queryString,int stmt_location,int stmt_len)407 DefineView(ViewStmt *stmt, const char *queryString,
408 int stmt_location, int stmt_len)
409 {
410 RawStmt *rawstmt;
411 Query *viewParse;
412 RangeVar *view;
413 ListCell *cell;
414 bool check_option;
415 ObjectAddress address;
416
417 /*
418 * Run parse analysis to convert the raw parse tree to a Query. Note this
419 * also acquires sufficient locks on the source table(s).
420 *
421 * Since parse analysis scribbles on its input, copy the raw parse tree;
422 * this ensures we don't corrupt a prepared statement, for example.
423 */
424 rawstmt = makeNode(RawStmt);
425 rawstmt->stmt = (Node *) copyObject(stmt->query);
426 rawstmt->stmt_location = stmt_location;
427 rawstmt->stmt_len = stmt_len;
428
429 viewParse = parse_analyze(rawstmt, queryString, NULL, 0, NULL);
430
431 /*
432 * The grammar should ensure that the result is a single SELECT Query.
433 * However, it doesn't forbid SELECT INTO, so we have to check for that.
434 */
435 if (!IsA(viewParse, Query))
436 elog(ERROR, "unexpected parse analysis result");
437 if (viewParse->utilityStmt != NULL &&
438 IsA(viewParse->utilityStmt, CreateTableAsStmt))
439 ereport(ERROR,
440 (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
441 errmsg("views must not contain SELECT INTO")));
442 if (viewParse->commandType != CMD_SELECT)
443 elog(ERROR, "unexpected parse analysis result");
444
445 /*
446 * Check for unsupported cases. These tests are redundant with ones in
447 * DefineQueryRewrite(), but that function will complain about a bogus ON
448 * SELECT rule, and we'd rather the message complain about a view.
449 */
450 if (viewParse->hasModifyingCTE)
451 ereport(ERROR,
452 (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
453 errmsg("views must not contain data-modifying statements in WITH")));
454
455 /*
456 * If the user specified the WITH CHECK OPTION, add it to the list of
457 * reloptions.
458 */
459 if (stmt->withCheckOption == LOCAL_CHECK_OPTION)
460 stmt->options = lappend(stmt->options,
461 makeDefElem("check_option",
462 (Node *) makeString("local"), -1));
463 else if (stmt->withCheckOption == CASCADED_CHECK_OPTION)
464 stmt->options = lappend(stmt->options,
465 makeDefElem("check_option",
466 (Node *) makeString("cascaded"), -1));
467
468 /*
469 * Check that the view is auto-updatable if WITH CHECK OPTION was
470 * specified.
471 */
472 check_option = false;
473
474 foreach(cell, stmt->options)
475 {
476 DefElem *defel = (DefElem *) lfirst(cell);
477
478 if (strcmp(defel->defname, "check_option") == 0)
479 check_option = true;
480 }
481
482 /*
483 * If the check option is specified, look to see if the view is actually
484 * auto-updatable or not.
485 */
486 if (check_option)
487 {
488 const char *view_updatable_error =
489 view_query_is_auto_updatable(viewParse, true);
490
491 if (view_updatable_error)
492 ereport(ERROR,
493 (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
494 errmsg("WITH CHECK OPTION is supported only on automatically updatable views"),
495 errhint("%s", _(view_updatable_error))));
496 }
497
498 /*
499 * If a list of column names was given, run through and insert these into
500 * the actual query tree. - thomas 2000-03-08
501 */
502 if (stmt->aliases != NIL)
503 {
504 ListCell *alist_item = list_head(stmt->aliases);
505 ListCell *targetList;
506
507 foreach(targetList, viewParse->targetList)
508 {
509 TargetEntry *te = lfirst_node(TargetEntry, targetList);
510
511 /* junk columns don't get aliases */
512 if (te->resjunk)
513 continue;
514 te->resname = pstrdup(strVal(lfirst(alist_item)));
515 alist_item = lnext(stmt->aliases, alist_item);
516 if (alist_item == NULL)
517 break; /* done assigning aliases */
518 }
519
520 if (alist_item != NULL)
521 ereport(ERROR,
522 (errcode(ERRCODE_SYNTAX_ERROR),
523 errmsg("CREATE VIEW specifies more column "
524 "names than columns")));
525 }
526
527 /* Unlogged views are not sensible. */
528 if (stmt->view->relpersistence == RELPERSISTENCE_UNLOGGED)
529 ereport(ERROR,
530 (errcode(ERRCODE_SYNTAX_ERROR),
531 errmsg("views cannot be unlogged because they do not have storage")));
532
533 /*
534 * If the user didn't explicitly ask for a temporary view, check whether
535 * we need one implicitly. We allow TEMP to be inserted automatically as
536 * long as the CREATE command is consistent with that --- no explicit
537 * schema name.
538 */
539 view = copyObject(stmt->view); /* don't corrupt original command */
540 if (view->relpersistence == RELPERSISTENCE_PERMANENT
541 && isQueryUsingTempRelation(viewParse))
542 {
543 view->relpersistence = RELPERSISTENCE_TEMP;
544 ereport(NOTICE,
545 (errmsg("view \"%s\" will be a temporary view",
546 view->relname)));
547 }
548
549 /*
550 * Create the view relation
551 *
552 * NOTE: if it already exists and replace is false, the xact will be
553 * aborted.
554 */
555 address = DefineVirtualRelation(view, viewParse->targetList,
556 stmt->replace, stmt->options, viewParse);
557
558 return address;
559 }
560
561 /*
562 * Use the rules system to store the query for the view.
563 */
564 void
StoreViewQuery(Oid viewOid,Query * viewParse,bool replace)565 StoreViewQuery(Oid viewOid, Query *viewParse, bool replace)
566 {
567 /*
568 * The range table of 'viewParse' does not contain entries for the "OLD"
569 * and "NEW" relations. So... add them!
570 */
571 viewParse = UpdateRangeTableOfViewParse(viewOid, viewParse);
572
573 /*
574 * Now create the rules associated with the view.
575 */
576 DefineViewRules(viewOid, viewParse, replace);
577 }
578