SQLite

      WhereLoop *p = pWInfo->pLoops;
      pWInfo->pLoops = p->pNextLoop;
      whereLoopDelete(db, p);
    }
    sqlite3DbFree(db, pWInfo);
  }
}

/*
** Compare every WhereLoop X on the list p against pTemplate.  If:
**
**    (1) both X and pTemplate refer to the same table, and
**    (2) both X and pTemplate use a single index, and
**    (3) pTemplate uses all the same WHERE clause terms as X plus
**        at least one more term,
**
** then make sure the cost pTemplate is less than the cost of X, adjusting
** the cost of pTemplate downward if necessary.
**
** Example: When computing the query plan for the SELECT below:
**
**     CREATE TABLE t1(a,b,c,d);
**     CREATE INDEX t1abc ON t1(a,b,c);
**     CREATE INDEX t1bc ON t1(b,c);
**     SELECT d FROM t1 WHERE a=? AND b=? AND c>=? ORDER BY c;
** 
** Make sure the cost of using three three columns of index t1abc is less
** than the cost of using both columns of t1bc.
*/
static void whereLoopAdjustCost(const WhereLoop *p, WhereLoop *pTemplate){
  if( (pTemplate->wsFlags & WHERE_INDEXED)==0 ) return;
  if( pTemplate->nLTerm==0 ) return;
  for(; p; p=p->pNextLoop){
    if( p->iTab==pTemplate->iTab
     && (p->wsFlags & WHERE_INDEXED)!=0
     && p->nLTerm<pTemplate->nLTerm
     && (p->rRun<pTemplate->rRun || (p->rRun==pTemplate->rRun &&
                                     p->nOut<=pTemplate->nOut))
    ){
      int i, j;
      for(j=0, i=p->nLTerm-1; i>=0 && j>=0; i--){
        for(j=pTemplate->nLTerm-1; j>=0; j--){
          if( pTemplate->aLTerm[j]==p->aLTerm[i] ) break;
        }
      }
      if( j>=0 ){
        pTemplate->rRun = p->rRun;
        pTemplate->nOut = p->nOut - 1;
      }
    }
  }
}

/*
** Search the list of WhereLoops in *ppPrev looking for one that can be
** supplanted by pTemplate.
**
** Return NULL if the WhereLoop list contains an entry that can supplant
** pTemplate, in other words if pTemplate does not belong on the list.

                 || p->rSetup==pTemplate->rSetup );

    /* whereLoopAddBtree() always generates and inserts the automatic index
    ** case first.  Hence compatible candidate WhereLoops never have a larger
    ** rSetup. Call this SETUP-INVARIANT */
    assert( p->rSetup>=pTemplate->rSetup );

    /* If existing WhereLoop p is better than pTemplate, pTemplate can be
    ** discarded.  WhereLoop p is better if:
    **   (1)  p has no more dependencies than pTemplate, and
    **   (2)  p has an equal or lower cost than pTemplate
    */
    if( (p->prereq & pTemplate->prereq)==p->prereq    /* (1)  */
     && p->rSetup<=pTemplate->rSetup                  /* (2a) */
     && p->rRun<=pTemplate->rRun                      /* (2b) */
     && p->nOut<=pTemplate->nOut                      /* (2c) */
    ){















      return 0;  /* Discard pTemplate */
    }

    /* If pTemplate is always better than p, then cause p to be overwritten
    ** with pTemplate.  pTemplate is better than p if:
    **   (1)  pTemplate has no more dependences than p, and
    **   (2)  pTemplate has an equal or lower cost than p.
    */
    if( (p->prereq & pTemplate->prereq)==pTemplate->prereq   /* (1)  */
     && p->rRun>=pTemplate->rRun                             /* (2a) */
     && p->nOut>=pTemplate->nOut                             /* (2b) */
    ){




      assert( p->rSetup>=pTemplate->rSetup ); /* SETUP-INVARIANT above */
      break;   /* Cause p to be overwritten by pTemplate */
    }
  }
  return ppPrev;
}

/*
** Insert or replace a WhereLoop entry using the template supplied.

** If pBuilder->pOrSet is not NULL then we care about only the
** prerequisites and rRun and nOut costs of the N best loops.  That
** information is gathered in the pBuilder->pOrSet object.  This special
** processing mode is used only for OR clause processing.
**
** When accumulating multiple loops (when pBuilder->pOrSet is NULL) we
** still might overwrite similar loops with the new template if the
** new template is better.  Loops may be overwritten if the following 
** conditions are met:
**
**    (1)  They have the same iTab.
**    (2)  They have the same iSortIdx.
**    (3)  The template has same or fewer dependencies than the current loop
**    (4)  The template has the same or lower cost than the current loop


*/
static int whereLoopInsert(WhereLoopBuilder *pBuilder, WhereLoop *pTemplate){
  WhereLoop **ppPrev, *p;
  WhereInfo *pWInfo = pBuilder->pWInfo;
  sqlite3 *db = pWInfo->pParse->db;

  /* If pBuilder->pOrSet is defined, then only keep track of the costs

    }
#endif
    return SQLITE_OK;
  }

  /* Look for an existing WhereLoop to replace with pTemplate
  */
  whereLoopAdjustCost(pWInfo->pLoops, pTemplate);
  ppPrev = whereLoopFindLesser(&pWInfo->pLoops, pTemplate);

  if( ppPrev==0 ){
    /* There already exists a WhereLoop on the list that is better
    ** than pTemplate, so just ignore pTemplate */
#if WHERETRACE_ENABLED /* 0x8 */
    if( sqlite3WhereTrace & 0x8 ){