src/backend/commands/view.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * view.c
   4  *        use rewrite rules to construct views
   5  *
   6  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
   7  * Portions Copyright (c) 1994, Regents of the University of California
   8  *
   9  *
  10  * IDENTIFICATION
  11  *        $PostgreSQL: pgsql/src/backend/commands/view.c,v 1.108 2008/12/06 23:22:46 momjian Exp $
  12  *
  13  *-------------------------------------------------------------------------
  14  */
  15 #include "postgres.h"
  16
  17 #include "access/heapam.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/rewriteManip.h"
  30 #include "rewrite/rewriteSupport.h"
  31 #include "utils/acl.h"
  32 #include "utils/lsyscache.h"
  33 #include "utils/rel.h"
  34
  35
  36 static void checkViewTupleDesc(TupleDesc newdesc, TupleDesc olddesc);
  37 static bool isViewOnTempTable_walker(Node *node, void *context);
  38
  39 /*---------------------------------------------------------------------
  40  * isViewOnTempTable
  41  *
  42  * Returns true iff any of the relations underlying this view are
  43  * temporary tables.
  44  *---------------------------------------------------------------------
  45  */
  46 static bool
  47 isViewOnTempTable(Query *viewParse)
  48 {
  49         return isViewOnTempTable_walker((Node *) viewParse, NULL);
  50 }
  51
  52 static bool
  53 isViewOnTempTable_walker(Node *node, void *context)
  54 {
  55         if (node == NULL)
  56                 return false;
  57
  58         if (IsA(node, Query))
  59         {
  60                 Query      *query = (Query *) node;
  61                 ListCell   *rtable;
  62
  63                 foreach(rtable, query->rtable)
  64                 {
  65                         RangeTblEntry *rte = lfirst(rtable);
  66
  67                         if (rte->rtekind == RTE_RELATION)
  68                         {
  69                                 Relation        rel = heap_open(rte->relid, AccessShareLock);
  70                                 bool            istemp = rel->rd_istemp;
  71
  72                                 heap_close(rel, AccessShareLock);
  73                                 if (istemp)
  74                                         return true;
  75                         }
  76                 }
  77
  78                 return query_tree_walker(query,
  79                                                                  isViewOnTempTable_walker,
  80                                                                  context,
  81                                                                  QTW_IGNORE_JOINALIASES);
  82         }
  83
  84         return expression_tree_walker(node,
  85                                                                   isViewOnTempTable_walker,
  86                                                                   context);
  87 }
  88
  89 /*---------------------------------------------------------------------
  90  * DefineVirtualRelation
  91  *
  92  * Create the "view" relation. `DefineRelation' does all the work,
  93  * we just provide the correct arguments ... at least when we're
  94  * creating a view.  If we're updating an existing view, we have to
  95  * work harder.
  96  *---------------------------------------------------------------------
  97  */
  98 static Oid
  99 DefineVirtualRelation(const RangeVar *relation, List *tlist, bool replace)
 100 {
 101         Oid                     viewOid,
 102                                 namespaceId;
 103         CreateStmt *createStmt = makeNode(CreateStmt);
 104         List       *attrList;
 105         ListCell   *t;
 106
 107         /*
 108          * create a list of ColumnDef nodes based on the names and types of the
 109          * (non-junk) targetlist items from the view's SELECT list.
 110          */
 111         attrList = NIL;
 112         foreach(t, tlist)
 113         {
 114                 TargetEntry *tle = lfirst(t);
 115
 116                 if (!tle->resjunk)
 117                 {
 118                         ColumnDef  *def = makeNode(ColumnDef);
 119
 120                         def->colname = pstrdup(tle->resname);
 121                         def->typename = makeTypeNameFromOid(exprType((Node *) tle->expr),
 122                                                                                          exprTypmod((Node *) tle->expr));
 123                         def->inhcount = 0;
 124                         def->is_local = true;
 125                         def->is_not_null = false;
 126                         def->raw_default = NULL;
 127                         def->cooked_default = NULL;
 128                         def->constraints = NIL;
 129
 130                         attrList = lappend(attrList, def);
 131                 }
 132         }
 133
 134         if (attrList == NIL)
 135                 ereport(ERROR,
 136                                 (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 137                                  errmsg("view must have at least one column")));
 138
 139         /*
 140          * Check to see if we want to replace an existing view.
 141          */
 142         namespaceId = RangeVarGetCreationNamespace(relation);
 143         viewOid = get_relname_relid(relation->relname, namespaceId);
 144
 145         if (OidIsValid(viewOid) && replace)
 146         {
 147                 Relation        rel;
 148                 TupleDesc       descriptor;
 149
 150                 /*
 151                  * Yes.  Get exclusive lock on the existing view ...
 152                  */
 153                 rel = relation_open(viewOid, AccessExclusiveLock);
 154
 155                 /*
 156                  * Make sure it *is* a view, and do permissions checks.
 157                  */
 158                 if (rel->rd_rel->relkind != RELKIND_VIEW)
 159                         ereport(ERROR,
 160                                         (errcode(ERRCODE_WRONG_OBJECT_TYPE),
 161                                          errmsg("\"%s\" is not a view",
 162                                                         RelationGetRelationName(rel))));
 163
 164                 if (!pg_class_ownercheck(viewOid, GetUserId()))
 165                         aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
 166                                                    RelationGetRelationName(rel));
 167
 168                 /*
 169                  * Due to the namespace visibility rules for temporary objects, we
 170                  * should only end up replacing a temporary view with another
 171                  * temporary view, and vice versa.
 172                  */
 173                 Assert(relation->istemp == rel->rd_istemp);
 174
 175                 /*
 176                  * If new attributes have been added, we must modify the pre-existing
 177                  * view.
 178                  */
 179                 if (list_length(attrList) > rel->rd_att->natts) {
 180                         List            *atcmds = NIL;
 181                         ListCell        *c;
 182                         int                     skip = rel->rd_att->natts;
 183
 184                         foreach(c, attrList) {
 185                                 AlterTableCmd *atcmd;
 186
 187                                 if (skip > 0) {
 188                                         --skip;
 189                                         continue;
 190                                 }
 191                                 atcmd = makeNode(AlterTableCmd);
 192                                 atcmd->subtype = AT_AddColumnToView;
 193                                 atcmd->def = lfirst(c);
 194                                 atcmds = lappend(atcmds, atcmd);
 195                         }
 196                         AlterTableInternal(viewOid, atcmds, true);
 197                 }
 198
 199                 /*
 200                  * Create a tuple descriptor to compare against the existing view, and
 201                  * verify that the old column list is an initial prefix of the new
 202                  * column list.
 203                  */
 204                 descriptor = BuildDescForRelation(attrList);
 205                 checkViewTupleDesc(descriptor, rel->rd_att);
 206
 207                 /*
 208                  * Seems okay, so return the OID of the pre-existing view.
 209                  */
 210                 relation_close(rel, NoLock);    /* keep the lock! */
 211
 212                 return viewOid;
 213         }
 214         else
 215         {
 216                 /*
 217                  * now set the parameters for keys/inheritance etc. All of these are
 218                  * uninteresting for views...
 219                  */
 220                 createStmt->relation = (RangeVar *) relation;
 221                 createStmt->tableElts = attrList;
 222                 createStmt->inhRelations = NIL;
 223                 createStmt->constraints = NIL;
 224                 createStmt->options = list_make1(defWithOids(false));
 225                 createStmt->oncommit = ONCOMMIT_NOOP;
 226                 createStmt->tablespacename = NULL;
 227
 228                 /*
 229                  * finally create the relation (this will error out if there's an
 230                  * existing view, so we don't need more code to complain if "replace"
 231                  * is false).
 232                  */
 233                 return DefineRelation(createStmt, RELKIND_VIEW);
 234         }
 235 }
 236
 237 /*
 238  * Verify that tupledesc associated with proposed new view definition
 239  * matches tupledesc of old view.  This is basically a cut-down version
 240  * of equalTupleDescs(), with code added to generate specific complaints.
 241  */
 242 static void
 243 checkViewTupleDesc(TupleDesc newdesc, TupleDesc olddesc)
 244 {
 245         int                     i;
 246
 247         if (newdesc->natts < olddesc->natts)
 248                 ereport(ERROR,
 249                                 (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 250                                  errmsg("cannot drop columns from view")));
 251         /* we can ignore tdhasoid */
 252
 253         for (i = 0; i < olddesc->natts; i++)
 254         {
 255                 Form_pg_attribute newattr = newdesc->attrs[i];
 256                 Form_pg_attribute oldattr = olddesc->attrs[i];
 257
 258                 /* XXX not right, but we don't support DROP COL on view anyway */
 259                 if (newattr->attisdropped != oldattr->attisdropped)
 260                         ereport(ERROR,
 261                                         (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 262                                          errmsg("cannot drop columns from view")));
 263
 264                 if (strcmp(NameStr(newattr->attname), NameStr(oldattr->attname)) != 0)
 265                         ereport(ERROR,
 266                                         (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 267                                          errmsg("cannot change name of view column \"%s\"",
 268                                                         NameStr(oldattr->attname))));
 269                 /* XXX would it be safe to allow atttypmod to change?  Not sure */
 270                 if (newattr->atttypid != oldattr->atttypid ||
 271                         newattr->atttypmod != oldattr->atttypmod)
 272                         ereport(ERROR,
 273                                         (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 274                                          errmsg("cannot change data type of view column \"%s\"",
 275                                                         NameStr(oldattr->attname))));
 276                 /* We can ignore the remaining attributes of an attribute... */
 277         }
 278
 279         /*
 280          * We ignore the constraint fields.  The new view desc can't have any
 281          * constraints, and the only ones that could be on the old view are
 282          * defaults, which we are happy to leave in place.
 283          */
 284 }
 285
 286 static void
 287 DefineViewRules(Oid viewOid, Query *viewParse, bool replace)
 288 {
 289         /*
 290          * Set up the ON SELECT rule.  Since the query has already been through
 291          * parse analysis, we use DefineQueryRewrite() directly.
 292          */
 293         DefineQueryRewrite(pstrdup(ViewSelectRuleName),
 294                                            viewOid,
 295                                            NULL,
 296                                            CMD_SELECT,
 297                                            true,
 298                                            replace,
 299                                            list_make1(viewParse));
 300
 301         /*
 302          * Someday: automatic ON INSERT, etc
 303          */
 304 }
 305
 306 /*---------------------------------------------------------------
 307  * UpdateRangeTableOfViewParse
 308  *
 309  * Update the range table of the given parsetree.
 310  * This update consists of adding two new entries IN THE BEGINNING
 311  * of the range table (otherwise the rule system will die a slow,
 312  * horrible and painful death, and we do not want that now, do we?)
 313  * one for the OLD relation and one for the NEW one (both of
 314  * them refer in fact to the "view" relation).
 315  *
 316  * Of course we must also increase the 'varnos' of all the Var nodes
 317  * by 2...
 318  *
 319  * These extra RT entries are not actually used in the query,
 320  * except for run-time permission checking.
 321  *---------------------------------------------------------------
 322  */
 323 static Query *
 324 UpdateRangeTableOfViewParse(Oid viewOid, Query *viewParse)
 325 {
 326         Relation        viewRel;
 327         List       *new_rt;
 328         RangeTblEntry *rt_entry1,
 329                            *rt_entry2;
 330
 331         /*
 332          * Make a copy of the given parsetree.  It's not so much that we don't
 333          * want to scribble on our input, it's that the parser has a bad habit of
 334          * outputting multiple links to the same subtree for constructs like
 335          * BETWEEN, and we mustn't have OffsetVarNodes increment the varno of a
 336          * Var node twice.      copyObject will expand any multiply-referenced subtree
 337          * into multiple copies.
 338          */
 339         viewParse = (Query *) copyObject(viewParse);
 340
 341         /* need to open the rel for addRangeTableEntryForRelation */
 342         viewRel = relation_open(viewOid, AccessShareLock);
 343
 344         /*
 345          * Create the 2 new range table entries and form the new range table...
 346          * OLD first, then NEW....
 347          */
 348         rt_entry1 = addRangeTableEntryForRelation(NULL, viewRel,
 349                                                                                           makeAlias("*OLD*", NIL),
 350                                                                                           false, false);
 351         rt_entry2 = addRangeTableEntryForRelation(NULL, viewRel,
 352                                                                                           makeAlias("*NEW*", NIL),
 353                                                                                           false, false);
 354         /* Must override addRangeTableEntry's default access-check flags */
 355         rt_entry1->requiredPerms = 0;
 356         rt_entry2->requiredPerms = 0;
 357
 358         new_rt = lcons(rt_entry1, lcons(rt_entry2, viewParse->rtable));
 359
 360         viewParse->rtable = new_rt;
 361
 362         /*
 363          * Now offset all var nodes by 2, and jointree RT indexes too.
 364          */
 365         OffsetVarNodes((Node *) viewParse, 2, 0);
 366
 367         relation_close(viewRel, AccessShareLock);
 368
 369         return viewParse;
 370 }
 371
 372 /*
 373  * DefineView
 374  *              Execute a CREATE VIEW command.
 375  */
 376 void
 377 DefineView(ViewStmt *stmt, const char *queryString)
 378 {
 379         Query      *viewParse;
 380         Oid                     viewOid;
 381         RangeVar   *view;
 382
 383         /*
 384          * Run parse analysis to convert the raw parse tree to a Query.  Note this
 385          * also acquires sufficient locks on the source table(s).
 386          *
 387          * Since parse analysis scribbles on its input, copy the raw parse tree;
 388          * this ensures we don't corrupt a prepared statement, for example.
 389          */
 390         viewParse = parse_analyze((Node *) copyObject(stmt->query),
 391                                                           queryString, NULL, 0);
 392
 393         /*
 394          * The grammar should ensure that the result is a single SELECT Query.
 395          */
 396         if (!IsA(viewParse, Query) ||
 397                 viewParse->commandType != CMD_SELECT)
 398                 elog(ERROR, "unexpected parse analysis result");
 399
 400         /*
 401          * If a list of column names was given, run through and insert these into
 402          * the actual query tree. - thomas 2000-03-08
 403          */
 404         if (stmt->aliases != NIL)
 405         {
 406                 ListCell   *alist_item = list_head(stmt->aliases);
 407                 ListCell   *targetList;
 408
 409                 foreach(targetList, viewParse->targetList)
 410                 {
 411                         TargetEntry *te = (TargetEntry *) lfirst(targetList);
 412
 413                         Assert(IsA(te, TargetEntry));
 414                         /* junk columns don't get aliases */
 415                         if (te->resjunk)
 416                                 continue;
 417                         te->resname = pstrdup(strVal(lfirst(alist_item)));
 418                         alist_item = lnext(alist_item);
 419                         if (alist_item == NULL)
 420                                 break;                  /* done assigning aliases */
 421                 }
 422
 423                 if (alist_item != NULL)
 424                         ereport(ERROR,
 425                                         (errcode(ERRCODE_SYNTAX_ERROR),
 426                                          errmsg("CREATE VIEW specifies more column "
 427                                                         "names than columns")));
 428         }
 429
 430         /*
 431          * If the user didn't explicitly ask for a temporary view, check whether
 432          * we need one implicitly.      We allow TEMP to be inserted automatically as
 433          * long as the CREATE command is consistent with that --- no explicit
 434          * schema name.
 435          */
 436         view = stmt->view;
 437         if (!view->istemp && isViewOnTempTable(viewParse))
 438         {
 439                 view = copyObject(view);        /* don't corrupt original command */
 440                 view->istemp = true;
 441                 ereport(NOTICE,
 442                                 (errmsg("view \"%s\" will be a temporary view",
 443                                                 view->relname)));
 444         }
 445
 446         /*
 447          * Create the view relation
 448          *
 449          * NOTE: if it already exists and replace is false, the xact will be
 450          * aborted.
 451          */
 452         viewOid = DefineVirtualRelation(view, viewParse->targetList,
 453                                                                         stmt->replace);
 454
 455         /*
 456          * The relation we have just created is not visible to any other commands
 457          * running with the same transaction & command id. So, increment the
 458          * command id counter (but do NOT pfree any memory!!!!)
 459          */
 460         CommandCounterIncrement();
 461
 462         /*
 463          * The range table of 'viewParse' does not contain entries for the "OLD"
 464          * and "NEW" relations. So... add them!
 465          */
 466         viewParse = UpdateRangeTableOfViewParse(viewOid, viewParse);
 467
 468         /*
 469          * Now create the rules associated with the view.
 470          */
 471         DefineViewRules(viewOid, viewParse, stmt->replace);
 472 }