make_join_rel.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * make_join_rel.c
   4  *        Routines copied from PostgreSQL core distribution.
   5  *
   6  * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
   7  * Portions Copyright (c) 1994, Regents of the University of California
   8  *
   9  *-------------------------------------------------------------------------
  10  */
  11
  12 /*
  13  * make_join_rel
  14  *         Find or create a join RelOptInfo that represents the join of
  15  *         the two given rels, and add to it path information for paths
  16  *         created with the two rels as outer and inner rel.
  17  *         (The join rel may already contain paths generated from other
  18  *         pairs of rels that add up to the same set of base rels.)
  19  *
  20  * NB: will return NULL if attempted join is not valid.  This can happen
  21  * when working with outer joins, or with IN or EXISTS clauses that have been
  22  * turned into joins.
  23  */
  24 RelOptInfo *
  25 make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2)
  26 {
  27         Relids          joinrelids;
  28         SpecialJoinInfo *sjinfo;
  29         bool            reversed;
  30         SpecialJoinInfo sjinfo_data;
  31         RelOptInfo *joinrel;
  32         List       *restrictlist;
  33
  34         /* We should never try to join two overlapping sets of rels. */
  35         Assert(!bms_overlap(rel1->relids, rel2->relids));
  36
  37         /* Construct Relids set that identifies the joinrel. */
  38         joinrelids = bms_union(rel1->relids, rel2->relids);
  39
  40         /* Check validity and determine join type. */
  41         if (!join_is_legal(root, rel1, rel2, joinrelids,
  42                                            &sjinfo, &reversed))
  43         {
  44                 /* invalid join path */
  45                 bms_free(joinrelids);
  46                 return NULL;
  47         }
  48
  49         /* Swap rels if needed to match the join info. */
  50         if (reversed)
  51         {
  52                 RelOptInfo *trel = rel1;
  53
  54                 rel1 = rel2;
  55                 rel2 = trel;
  56         }
  57
  58         /*
  59          * If it's a plain inner join, then we won't have found anything in
  60          * join_info_list.      Make up a SpecialJoinInfo so that selectivity
  61          * estimation functions will know what's being joined.
  62          */
  63         if (sjinfo == NULL)
  64         {
  65                 sjinfo = &sjinfo_data;
  66                 sjinfo->type = T_SpecialJoinInfo;
  67                 sjinfo->min_lefthand = rel1->relids;
  68                 sjinfo->min_righthand = rel2->relids;
  69                 sjinfo->syn_lefthand = rel1->relids;
  70                 sjinfo->syn_righthand = rel2->relids;
  71                 sjinfo->jointype = JOIN_INNER;
  72                 /* we don't bother trying to make the remaining fields valid */
  73                 sjinfo->lhs_strict = false;
  74                 sjinfo->delay_upper_joins = false;
  75                 sjinfo->join_quals = NIL;
  76         }
  77
  78         /*
  79          * Find or build the join RelOptInfo, and compute the restrictlist that
  80          * goes with this particular joining.
  81          */
  82         joinrel = build_join_rel(root, joinrelids, rel1, rel2, sjinfo,
  83                                                          &restrictlist);
  84
  85         /*
  86          * If we've already proven this join is empty, we needn't consider any
  87          * more paths for it.
  88          */
  89         if (is_dummy_rel(joinrel))
  90         {
  91                 bms_free(joinrelids);
  92                 return joinrel;
  93         }
  94
  95         /*
  96          * Consider paths using each rel as both outer and inner.  Depending on
  97          * the join type, a provably empty outer or inner rel might mean the join
  98          * is provably empty too; in which case throw away any previously computed
  99          * paths and mark the join as dummy.  (We do it this way since it's
 100          * conceivable that dummy-ness of a multi-element join might only be
 101          * noticeable for certain construction paths.)
 102          *
 103          * Also, a provably constant-false join restriction typically means that
 104          * we can skip evaluating one or both sides of the join.  We do this by
 105          * marking the appropriate rel as dummy.  For outer joins, a
 106          * constant-false restriction that is pushed down still means the whole
 107          * join is dummy, while a non-pushed-down one means that no inner rows
 108          * will join so we can treat the inner rel as dummy.
 109          *
 110          * We need only consider the jointypes that appear in join_info_list, plus
 111          * JOIN_INNER.
 112          */
 113         switch (sjinfo->jointype)
 114         {
 115                 case JOIN_INNER:
 116                         if (is_dummy_rel(rel1) || is_dummy_rel(rel2) ||
 117                                 restriction_is_constant_false(restrictlist, false))
 118                         {
 119                                 mark_dummy_rel(joinrel);
 120                                 break;
 121                         }
 122                         add_paths_to_joinrel(root, joinrel, rel1, rel2,
 123                                                                  JOIN_INNER, sjinfo,
 124                                                                  restrictlist);
 125                         add_paths_to_joinrel(root, joinrel, rel2, rel1,
 126                                                                  JOIN_INNER, sjinfo,
 127                                                                  restrictlist);
 128                         break;
 129                 case JOIN_LEFT:
 130                         if (is_dummy_rel(rel1) ||
 131                                 restriction_is_constant_false(restrictlist, true))
 132                         {
 133                                 mark_dummy_rel(joinrel);
 134                                 break;
 135                         }
 136                         if (restriction_is_constant_false(restrictlist, false) &&
 137                                 bms_is_subset(rel2->relids, sjinfo->syn_righthand))
 138                                 mark_dummy_rel(rel2);
 139                         add_paths_to_joinrel(root, joinrel, rel1, rel2,
 140                                                                  JOIN_LEFT, sjinfo,
 141                                                                  restrictlist);
 142                         add_paths_to_joinrel(root, joinrel, rel2, rel1,
 143                                                                  JOIN_RIGHT, sjinfo,
 144                                                                  restrictlist);
 145                         break;
 146                 case JOIN_FULL:
 147                         if ((is_dummy_rel(rel1) && is_dummy_rel(rel2)) ||
 148                                 restriction_is_constant_false(restrictlist, true))
 149                         {
 150                                 mark_dummy_rel(joinrel);
 151                                 break;
 152                         }
 153                         add_paths_to_joinrel(root, joinrel, rel1, rel2,
 154                                                                  JOIN_FULL, sjinfo,
 155                                                                  restrictlist);
 156                         add_paths_to_joinrel(root, joinrel, rel2, rel1,
 157                                                                  JOIN_FULL, sjinfo,
 158                                                                  restrictlist);
 159
 160                         /*
 161                          * If there are join quals that aren't mergeable or hashable, we
 162                          * may not be able to build any valid plan.  Complain here so that
 163                          * we can give a somewhat-useful error message.  (Since we have no
 164                          * flexibility of planning for a full join, there's no chance of
 165                          * succeeding later with another pair of input rels.)
 166                          */
 167                         if (joinrel->pathlist == NIL)
 168                                 ereport(ERROR,
 169                                                 (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 170                                                  errmsg("FULL JOIN is only supported with merge-joinable or hash-joinable join conditions")));
 171                         break;
 172                 case JOIN_SEMI:
 173
 174                         /*
 175                          * We might have a normal semijoin, or a case where we don't have
 176                          * enough rels to do the semijoin but can unique-ify the RHS and
 177                          * then do an innerjoin (see comments in join_is_legal).  In the
 178                          * latter case we can't apply JOIN_SEMI joining.
 179                          */
 180                         if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
 181                                 bms_is_subset(sjinfo->min_righthand, rel2->relids))
 182                         {
 183                                 if (is_dummy_rel(rel1) || is_dummy_rel(rel2) ||
 184                                         restriction_is_constant_false(restrictlist, false))
 185                                 {
 186                                         mark_dummy_rel(joinrel);
 187                                         break;
 188                                 }
 189                                 add_paths_to_joinrel(root, joinrel, rel1, rel2,
 190                                                                          JOIN_SEMI, sjinfo,
 191                                                                          restrictlist);
 192                         }
 193
 194                         /*
 195                          * If we know how to unique-ify the RHS and one input rel is
 196                          * exactly the RHS (not a superset) we can consider unique-ifying
 197                          * it and then doing a regular join.  (The create_unique_path
 198                          * check here is probably redundant with what join_is_legal did,
 199                          * but if so the check is cheap because it's cached.  So test
 200                          * anyway to be sure.)
 201                          */
 202                         if (bms_equal(sjinfo->syn_righthand, rel2->relids) &&
 203                                 create_unique_path(root, rel2, rel2->cheapest_total_path,
 204                                                                    sjinfo) != NULL)
 205                         {
 206                                 if (is_dummy_rel(rel1) || is_dummy_rel(rel2) ||
 207                                         restriction_is_constant_false(restrictlist, false))
 208                                 {
 209                                         mark_dummy_rel(joinrel);
 210                                         break;
 211                                 }
 212                                 add_paths_to_joinrel(root, joinrel, rel1, rel2,
 213                                                                          JOIN_UNIQUE_INNER, sjinfo,
 214                                                                          restrictlist);
 215                                 add_paths_to_joinrel(root, joinrel, rel2, rel1,
 216                                                                          JOIN_UNIQUE_OUTER, sjinfo,
 217                                                                          restrictlist);
 218                         }
 219                         break;
 220                 case JOIN_ANTI:
 221                         if (is_dummy_rel(rel1) ||
 222                                 restriction_is_constant_false(restrictlist, true))
 223                         {
 224                                 mark_dummy_rel(joinrel);
 225                                 break;
 226                         }
 227                         if (restriction_is_constant_false(restrictlist, false) &&
 228                                 bms_is_subset(rel2->relids, sjinfo->syn_righthand))
 229                                 mark_dummy_rel(rel2);
 230                         add_paths_to_joinrel(root, joinrel, rel1, rel2,
 231                                                                  JOIN_ANTI, sjinfo,
 232                                                                  restrictlist);
 233                         break;
 234                 default:
 235                         /* other values not expected here */
 236                         elog(ERROR, "unrecognized join type: %d", (int) sjinfo->jointype);
 237                         break;
 238         }
 239
 240         bms_free(joinrelids);
 241
 242         return joinrel;
 243 }