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  *        $PostgreSQL$
  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                  * Create a tuple descriptor to compare against the existing view, and
 177                  * verify it matches.
 178                  */
 179                 descriptor = BuildDescForRelation(attrList);
 180                 checkViewTupleDesc(descriptor, rel->rd_att);
 181
 182                 /*
 183                  * Seems okay, so return the OID of the pre-existing view.
 184                  */
 185                 relation_close(rel, NoLock);    /* keep the lock! */
 186
 187                 return viewOid;
 188         }
 189         else
 190         {
 191                 /*
 192                  * now set the parameters for keys/inheritance etc. All of these are
 193                  * uninteresting for views...
 194                  */
 195                 createStmt->relation = (RangeVar *) relation;
 196                 createStmt->tableElts = attrList;
 197                 createStmt->inhRelations = NIL;
 198                 createStmt->constraints = NIL;
 199                 createStmt->options = list_make1(defWithOids(false));
 200                 createStmt->oncommit = ONCOMMIT_NOOP;
 201                 createStmt->tablespacename = NULL;
 202
 203                 /*
 204                  * finally create the relation (this will error out if there's an
 205                  * existing view, so we don't need more code to complain if "replace"
 206                  * is false).
 207                  */
 208                 return DefineRelation(createStmt, RELKIND_VIEW);
 209         }
 210 }
 211
 212 /*
 213  * Verify that tupledesc associated with proposed new view definition
 214  * matches tupledesc of old view.  This is basically a cut-down version
 215  * of equalTupleDescs(), with code added to generate specific complaints.
 216  */
 217 static void
 218 checkViewTupleDesc(TupleDesc newdesc, TupleDesc olddesc)
 219 {
 220         int                     i;
 221
 222         if (newdesc->natts != olddesc->natts)
 223                 ereport(ERROR,
 224                                 (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 225                                  errmsg("cannot change number of columns in view")));
 226         /* we can ignore tdhasoid */
 227
 228         for (i = 0; i < newdesc->natts; i++)
 229         {
 230                 Form_pg_attribute newattr = newdesc->attrs[i];
 231                 Form_pg_attribute oldattr = olddesc->attrs[i];
 232
 233                 /* XXX not right, but we don't support DROP COL on view anyway */
 234                 if (newattr->attisdropped != oldattr->attisdropped)
 235                         ereport(ERROR,
 236                                         (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 237                                          errmsg("cannot change number of columns in view")));
 238
 239                 if (strcmp(NameStr(newattr->attname), NameStr(oldattr->attname)) != 0)
 240                         ereport(ERROR,
 241                                         (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 242                                          errmsg("cannot change name of view column \"%s\"",
 243                                                         NameStr(oldattr->attname))));
 244                 /* XXX would it be safe to allow atttypmod to change?  Not sure */
 245                 if (newattr->atttypid != oldattr->atttypid ||
 246                         newattr->atttypmod != oldattr->atttypmod)
 247                         ereport(ERROR,
 248                                         (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 249                                          errmsg("cannot change data type of view column \"%s\"",
 250                                                         NameStr(oldattr->attname))));
 251                 /* We can ignore the remaining attributes of an attribute... */
 252         }
 253
 254         /*
 255          * We ignore the constraint fields.  The new view desc can't have any
 256          * constraints, and the only ones that could be on the old view are
 257          * defaults, which we are happy to leave in place.
 258          */
 259 }
 260
 261 static void
 262 DefineViewRules(Oid viewOid, Query *viewParse, bool replace)
 263 {
 264         /*
 265          * Set up the ON SELECT rule.  Since the query has already been through
 266          * parse analysis, we use DefineQueryRewrite() directly.
 267          */
 268         DefineQueryRewrite(pstrdup(ViewSelectRuleName),
 269                                            viewOid,
 270                                            NULL,
 271                                            CMD_SELECT,
 272                                            true,
 273                                            replace,
 274                                            list_make1(viewParse));
 275
 276         /*
 277          * Someday: automatic ON INSERT, etc
 278          */
 279 }
 280
 281 /*---------------------------------------------------------------
 282  * UpdateRangeTableOfViewParse
 283  *
 284  * Update the range table of the given parsetree.
 285  * This update consists of adding two new entries IN THE BEGINNING
 286  * of the range table (otherwise the rule system will die a slow,
 287  * horrible and painful death, and we do not want that now, do we?)
 288  * one for the OLD relation and one for the NEW one (both of
 289  * them refer in fact to the "view" relation).
 290  *
 291  * Of course we must also increase the 'varnos' of all the Var nodes
 292  * by 2...
 293  *
 294  * These extra RT entries are not actually used in the query,
 295  * except for run-time permission checking.
 296  *---------------------------------------------------------------
 297  */
 298 static Query *
 299 UpdateRangeTableOfViewParse(Oid viewOid, Query *viewParse)
 300 {
 301         Relation        viewRel;
 302         List       *new_rt;
 303         RangeTblEntry *rt_entry1,
 304                            *rt_entry2;
 305
 306         /*
 307          * Make a copy of the given parsetree.  It's not so much that we don't
 308          * want to scribble on our input, it's that the parser has a bad habit of
 309          * outputting multiple links to the same subtree for constructs like
 310          * BETWEEN, and we mustn't have OffsetVarNodes increment the varno of a
 311          * Var node twice.      copyObject will expand any multiply-referenced subtree
 312          * into multiple copies.
 313          */
 314         viewParse = (Query *) copyObject(viewParse);
 315
 316         /* need to open the rel for addRangeTableEntryForRelation */
 317         viewRel = relation_open(viewOid, AccessShareLock);
 318
 319         /*
 320          * Create the 2 new range table entries and form the new range table...
 321          * OLD first, then NEW....
 322          */
 323         rt_entry1 = addRangeTableEntryForRelation(NULL, viewRel,
 324                                                                                           makeAlias("*OLD*", NIL),
 325                                                                                           false, false);
 326         rt_entry2 = addRangeTableEntryForRelation(NULL, viewRel,
 327                                                                                           makeAlias("*NEW*", NIL),
 328                                                                                           false, false);
 329         /* Must override addRangeTableEntry's default access-check flags */
 330         rt_entry1->requiredPerms = 0;
 331         rt_entry2->requiredPerms = 0;
 332
 333         new_rt = lcons(rt_entry1, lcons(rt_entry2, viewParse->rtable));
 334
 335         viewParse->rtable = new_rt;
 336
 337         /*
 338          * Now offset all var nodes by 2, and jointree RT indexes too.
 339          */
 340         OffsetVarNodes((Node *) viewParse, 2, 0);
 341
 342         relation_close(viewRel, AccessShareLock);
 343
 344         return viewParse;
 345 }
 346
 347 /*
 348  * DefineView
 349  *              Execute a CREATE VIEW command.
 350  */
 351 void
 352 DefineView(ViewStmt *stmt, const char *queryString)
 353 {
 354         Query      *viewParse;
 355         Oid                     viewOid;
 356         RangeVar   *view;
 357
 358         /*
 359          * Run parse analysis to convert the raw parse tree to a Query.  Note this
 360          * also acquires sufficient locks on the source table(s).
 361          *
 362          * Since parse analysis scribbles on its input, copy the raw parse tree;
 363          * this ensures we don't corrupt a prepared statement, for example.
 364          */
 365         viewParse = parse_analyze((Node *) copyObject(stmt->query),
 366                                                           queryString, NULL, 0);
 367
 368         /*
 369          * The grammar should ensure that the result is a single SELECT Query.
 370          */
 371         if (!IsA(viewParse, Query) ||
 372                 viewParse->commandType != CMD_SELECT)
 373                 elog(ERROR, "unexpected parse analysis result");
 374
 375         /*
 376          * If a list of column names was given, run through and insert these into
 377          * the actual query tree. - thomas 2000-03-08
 378          */
 379         if (stmt->aliases != NIL)
 380         {
 381                 ListCell   *alist_item = list_head(stmt->aliases);
 382                 ListCell   *targetList;
 383
 384                 foreach(targetList, viewParse->targetList)
 385                 {
 386                         TargetEntry *te = (TargetEntry *) lfirst(targetList);
 387
 388                         Assert(IsA(te, TargetEntry));
 389                         /* junk columns don't get aliases */
 390                         if (te->resjunk)
 391                                 continue;
 392                         te->resname = pstrdup(strVal(lfirst(alist_item)));
 393                         alist_item = lnext(alist_item);
 394                         if (alist_item == NULL)
 395                                 break;                  /* done assigning aliases */
 396                 }
 397
 398                 if (alist_item != NULL)
 399                         ereport(ERROR,
 400                                         (errcode(ERRCODE_SYNTAX_ERROR),
 401                                          errmsg("CREATE VIEW specifies more column "
 402                                                         "names than columns")));
 403         }
 404
 405         /*
 406          * If the user didn't explicitly ask for a temporary view, check whether
 407          * we need one implicitly.      We allow TEMP to be inserted automatically as
 408          * long as the CREATE command is consistent with that --- no explicit
 409          * schema name.
 410          */
 411         view = stmt->view;
 412         if (!view->istemp && isViewOnTempTable(viewParse))
 413         {
 414                 view = copyObject(view);        /* don't corrupt original command */
 415                 view->istemp = true;
 416                 ereport(NOTICE,
 417                                 (errmsg("view \"%s\" will be a temporary view",
 418                                                 view->relname)));
 419         }
 420
 421         /*
 422          * Create the view relation
 423          *
 424          * NOTE: if it already exists and replace is false, the xact will be
 425          * aborted.
 426          */
 427         viewOid = DefineVirtualRelation(view, viewParse->targetList,
 428                                                                         stmt->replace);
 429
 430         /*
 431          * The relation we have just created is not visible to any other commands
 432          * running with the same transaction & command id. So, increment the
 433          * command id counter (but do NOT pfree any memory!!!!)
 434          */
 435         CommandCounterIncrement();
 436
 437         /*
 438          * The range table of 'viewParse' does not contain entries for the "OLD"
 439          * and "NEW" relations. So... add them!
 440          */
 441         viewParse = UpdateRangeTableOfViewParse(viewOid, viewParse);
 442
 443         /*
 444          * Now create the rules associated with the view.
 445          */
 446         DefineViewRules(viewOid, viewParse, stmt->replace);
 447 }