src/backend/optimizer/prep/preptlist.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * preptlist.c
   4  *        Routines to preprocess the parse tree target list
   5  *
   6  * This module takes care of altering the query targetlist as needed for
   7  * INSERT, UPDATE, and DELETE queries.  For INSERT and UPDATE queries,
   8  * the targetlist must contain an entry for each attribute of the target
   9  * relation in the correct order.  For both UPDATE and DELETE queries,
  10  * we need a junk targetlist entry holding the CTID attribute --- the
  11  * executor relies on this to find the tuple to be replaced/deleted.
  12  *
  13  *
  14  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  15  * Portions Copyright (c) 1994, Regents of the University of California
  16  *
  17  * IDENTIFICATION
  18  *        $PostgreSQL: pgsql/src/backend/optimizer/prep/preptlist.c,v 1.79 2005/11/22 18:17:14 momjian Exp $
  19  *
  20  *-------------------------------------------------------------------------
  21  */
  22
  23 #include "postgres.h"
  24
  25 #include "access/heapam.h"
  26 #include "catalog/pg_type.h"
  27 #include "nodes/makefuncs.h"
  28 #include "optimizer/prep.h"
  29 #include "optimizer/subselect.h"
  30 #include "parser/analyze.h"
  31 #include "parser/parsetree.h"
  32 #include "parser/parse_coerce.h"
  33
  34
  35 static List *expand_targetlist(List *tlist, int command_type,
  36                                   Index result_relation, List *range_table);
  37
  38
  39 /*
  40  * preprocess_targetlist
  41  *        Driver for preprocessing the parse tree targetlist.
  42  *
  43  *        Returns the new targetlist.
  44  */
  45 List *
  46 preprocess_targetlist(PlannerInfo *root, List *tlist)
  47 {
  48         Query      *parse = root->parse;
  49         int                     result_relation = parse->resultRelation;
  50         List       *range_table = parse->rtable;
  51         CmdType         command_type = parse->commandType;
  52
  53         /*
  54          * Sanity check: if there is a result relation, it'd better be a real
  55          * relation not a subquery.  Else parser or rewriter messed up.
  56          */
  57         if (result_relation)
  58         {
  59                 RangeTblEntry *rte = rt_fetch(result_relation, range_table);
  60
  61                 if (rte->subquery != NULL || rte->relid == InvalidOid)
  62                         elog(ERROR, "subquery cannot be result relation");
  63         }
  64
  65         /*
  66          * for heap_formtuple to work, the targetlist must match the exact order
  67          * of the attributes. We also need to fill in any missing attributes. -ay
  68          * 10/94
  69          */
  70         if (command_type == CMD_INSERT || command_type == CMD_UPDATE)
  71                 tlist = expand_targetlist(tlist, command_type,
  72                                                                   result_relation, range_table);
  73
  74         /*
  75          * for "update" and "delete" queries, add ctid of the result relation into
  76          * the target list so that the ctid will propagate through execution and
  77          * ExecutePlan() will be able to identify the right tuple to replace or
  78          * delete.      This extra field is marked "junk" so that it is not stored
  79          * back into the tuple.
  80          */
  81         if (command_type == CMD_UPDATE || command_type == CMD_DELETE)
  82         {
  83                 TargetEntry *tle;
  84                 Var                *var;
  85
  86                 var = makeVar(result_relation, SelfItemPointerAttributeNumber,
  87                                           TIDOID, -1, 0);
  88
  89                 tle = makeTargetEntry((Expr *) var,
  90                                                           list_length(tlist) + 1,
  91                                                           pstrdup("ctid"),
  92                                                           true);
  93
  94                 /*
  95                  * For an UPDATE, expand_targetlist already created a fresh tlist. For
  96                  * DELETE, better do a listCopy so that we don't destructively modify
  97                  * the original tlist (is this really necessary?).
  98                  */
  99                 if (command_type == CMD_DELETE)
 100                         tlist = list_copy(tlist);
 101
 102                 tlist = lappend(tlist, tle);
 103         }
 104
 105         /*
 106          * Add TID targets for rels selected FOR UPDATE/SHARE.  The executor uses
 107          * the TID to know which rows to lock, much as for UPDATE or DELETE.
 108          */
 109         if (parse->rowMarks)
 110         {
 111                 ListCell   *l;
 112
 113                 /*
 114                  * We've got trouble if the FOR UPDATE/SHARE appears inside grouping,
 115                  * since grouping renders a reference to individual tuple CTIDs
 116                  * invalid.  This is also checked at parse time, but that's
 117                  * insufficient because of rule substitution, query pullup, etc.
 118                  */
 119                 CheckSelectLocking(parse, parse->forUpdate);
 120
 121                 /*
 122                  * Currently the executor only supports FOR UPDATE/SHARE at top level
 123                  */
 124                 if (PlannerQueryLevel > 1)
 125                         ereport(ERROR,
 126                                         (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 127                         errmsg("SELECT FOR UPDATE/SHARE is not allowed in subqueries")));
 128
 129                 foreach(l, parse->rowMarks)
 130                 {
 131                         Index           rti = lfirst_int(l);
 132                         Var                *var;
 133                         char       *resname;
 134                         TargetEntry *tle;
 135
 136                         var = makeVar(rti,
 137                                                   SelfItemPointerAttributeNumber,
 138                                                   TIDOID,
 139                                                   -1,
 140                                                   0);
 141
 142                         resname = (char *) palloc(32);
 143                         snprintf(resname, 32, "ctid%u", rti);
 144
 145                         tle = makeTargetEntry((Expr *) var,
 146                                                                   list_length(tlist) + 1,
 147                                                                   resname,
 148                                                                   true);
 149
 150                         tlist = lappend(tlist, tle);
 151                 }
 152         }
 153
 154         return tlist;
 155 }
 156
 157 /*****************************************************************************
 158  *
 159  *              TARGETLIST EXPANSION
 160  *
 161  *****************************************************************************/
 162
 163 /*
 164  * expand_targetlist
 165  *        Given a target list as generated by the parser and a result relation,
 166  *        add targetlist entries for any missing attributes, and ensure the
 167  *        non-junk attributes appear in proper field order.
 168  *
 169  * NOTE: if you are tempted to put more processing here, consider whether
 170  * it shouldn't go in the rewriter's rewriteTargetList() instead.
 171  */
 172 static List *
 173 expand_targetlist(List *tlist, int command_type,
 174                                   Index result_relation, List *range_table)
 175 {
 176         List       *new_tlist = NIL;
 177         ListCell   *tlist_item;
 178         Relation        rel;
 179         int                     attrno,
 180                                 numattrs;
 181
 182         tlist_item = list_head(tlist);
 183
 184         /*
 185          * The rewriter should have already ensured that the TLEs are in correct
 186          * order; but we have to insert TLEs for any missing attributes.
 187          *
 188          * Scan the tuple description in the relation's relcache entry to make
 189          * sure we have all the user attributes in the right order.  We assume
 190          * that the rewriter already acquired at least AccessShareLock on the
 191          * relation, so we need no lock here.
 192          */
 193         rel = heap_open(getrelid(result_relation, range_table), NoLock);
 194
 195         numattrs = RelationGetNumberOfAttributes(rel);
 196
 197         for (attrno = 1; attrno <= numattrs; attrno++)
 198         {
 199                 Form_pg_attribute att_tup = rel->rd_att->attrs[attrno - 1];
 200                 TargetEntry *new_tle = NULL;
 201
 202                 if (tlist_item != NULL)
 203                 {
 204                         TargetEntry *old_tle = (TargetEntry *) lfirst(tlist_item);
 205
 206                         if (!old_tle->resjunk && old_tle->resno == attrno)
 207                         {
 208                                 new_tle = old_tle;
 209                                 tlist_item = lnext(tlist_item);
 210                         }
 211                 }
 212
 213                 if (new_tle == NULL)
 214                 {
 215                         /*
 216                          * Didn't find a matching tlist entry, so make one.
 217                          *
 218                          * For INSERT, generate a NULL constant.  (We assume the rewriter
 219                          * would have inserted any available default value.) Also, if the
 220                          * column isn't dropped, apply any domain constraints that might
 221                          * exist --- this is to catch domain NOT NULL.
 222                          *
 223                          * For UPDATE, generate a Var reference to the existing value of
 224                          * the attribute, so that it gets copied to the new tuple. But
 225                          * generate a NULL for dropped columns (we want to drop any old
 226                          * values).
 227                          *
 228                          * When generating a NULL constant for a dropped column, we label
 229                          * it INT4 (any other guaranteed-to-exist datatype would do as
 230                          * well). We can't label it with the dropped column's datatype
 231                          * since that might not exist anymore.  It does not really matter
 232                          * what we claim the type is, since NULL is NULL --- its
 233                          * representation is datatype-independent.      This could perhaps
 234                          * confuse code comparing the finished plan to the target
 235                          * relation, however.
 236                          */
 237                         Oid                     atttype = att_tup->atttypid;
 238                         int32           atttypmod = att_tup->atttypmod;
 239                         Node       *new_expr;
 240
 241                         switch (command_type)
 242                         {
 243                                 case CMD_INSERT:
 244                                         if (!att_tup->attisdropped)
 245                                         {
 246                                                 new_expr = (Node *) makeConst(atttype,
 247                                                                                                           att_tup->attlen,
 248                                                                                                           (Datum) 0,
 249                                                                                                           true,         /* isnull */
 250                                                                                                           att_tup->attbyval);
 251                                                 new_expr = coerce_to_domain(new_expr,
 252                                                                                                         InvalidOid,
 253                                                                                                         atttype,
 254                                                                                                         COERCE_IMPLICIT_CAST,
 255                                                                                                         false,
 256                                                                                                         false);
 257                                         }
 258                                         else
 259                                         {
 260                                                 /* Insert NULL for dropped column */
 261                                                 new_expr = (Node *) makeConst(INT4OID,
 262                                                                                                           sizeof(int32),
 263                                                                                                           (Datum) 0,
 264                                                                                                           true,         /* isnull */
 265                                                                                                           true /* byval */ );
 266                                         }
 267                                         break;
 268                                 case CMD_UPDATE:
 269                                         if (!att_tup->attisdropped)
 270                                         {
 271                                                 new_expr = (Node *) makeVar(result_relation,
 272                                                                                                         attrno,
 273                                                                                                         atttype,
 274                                                                                                         atttypmod,
 275                                                                                                         0);
 276                                         }
 277                                         else
 278                                         {
 279                                                 /* Insert NULL for dropped column */
 280                                                 new_expr = (Node *) makeConst(INT4OID,
 281                                                                                                           sizeof(int32),
 282                                                                                                           (Datum) 0,
 283                                                                                                           true,         /* isnull */
 284                                                                                                           true /* byval */ );
 285                                         }
 286                                         break;
 287                                 default:
 288                                         elog(ERROR, "unrecognized command_type: %d",
 289                                                  (int) command_type);
 290                                         new_expr = NULL;        /* keep compiler quiet */
 291                                         break;
 292                         }
 293
 294                         new_tle = makeTargetEntry((Expr *) new_expr,
 295                                                                           attrno,
 296                                                                           pstrdup(NameStr(att_tup->attname)),
 297                                                                           false);
 298                 }
 299
 300                 new_tlist = lappend(new_tlist, new_tle);
 301         }
 302
 303         /*
 304          * The remaining tlist entries should be resjunk; append them all to the
 305          * end of the new tlist, making sure they have resnos higher than the last
 306          * real attribute.      (Note: although the rewriter already did such
 307          * renumbering, we have to do it again here in case we are doing an UPDATE
 308          * in a table with dropped columns, or an inheritance child table with
 309          * extra columns.)
 310          */
 311         while (tlist_item)
 312         {
 313                 TargetEntry *old_tle = (TargetEntry *) lfirst(tlist_item);
 314
 315                 if (!old_tle->resjunk)
 316                         elog(ERROR, "targetlist is not sorted correctly");
 317                 /* Get the resno right, but don't copy unnecessarily */
 318                 if (old_tle->resno != attrno)
 319                 {
 320                         old_tle = flatCopyTargetEntry(old_tle);
 321                         old_tle->resno = attrno;
 322                 }
 323                 new_tlist = lappend(new_tlist, old_tle);
 324                 attrno++;
 325                 tlist_item = lnext(tlist_item);
 326         }
 327
 328         heap_close(rel, NoLock);
 329
 330         return new_tlist;
 331 }