SQLite

  sqlite3DebugPrintf("%c %2d.%0*llx.%0*llx", p->cId,
                     p->iTab, nb, p->maskSelf, nb, p->prereq);
  sqlite3DebugPrintf(" %8s",
                     pItem->zAlias ? pItem->zAlias : pTab->zName);
  if( (p->wsFlags & WHERE_VIRTUALTABLE)==0 ){
    if( p->u.btree.pIndex ){
      const char *zName = p->u.btree.pIndex->zName;
      if( zName==0 ) zName = "ipk";
      if( strncmp(zName, "sqlite_autoindex_", 17)==0 ){
        int i = sqlite3Strlen30(zName) - 1;
        while( zName[i]!='_' ) i--;
        zName += i;
      }
      sqlite3DebugPrintf(".%-12s %2d", zName, p->u.btree.nEq);
    }else{

  ** best WhereLoop.  pBuilder->pBest->maskSelf==0 indicates that no
  ** prior WhereLoops have been evaluated and that the current pTemplate
  ** is therefore the first and hence the best and should be retained.
  */
  if( (p = pBuilder->pBest)!=0 ){
    if( p->maskSelf!=0 ){
      if( p->rRun+p->rSetup < pTemplate->rRun+pTemplate->rSetup ){
        goto whereLoopInsert_noop;
      }
      if( p->rRun+p->rSetup == pTemplate->rRun+pTemplate->rSetup
       && p->prereq <= pTemplate->prereq ){
        goto whereLoopInsert_noop;
      }
    }
    *p = *pTemplate;
    p->aTerm = 0;
    p->u.vtab.needFree = 0;
#if WHERETRACE_ENABLED
    if( sqlite3WhereTrace & 0x8 ){
      sqlite3DebugPrintf("ins-best: ");
      whereLoopPrint(pTemplate, pBuilder->pTabList);
    }
#endif
    return SQLITE_OK;
  }

  /* Search for an existing WhereLoop to overwrite, or which takes
  ** priority over pTemplate.
  */
  for(ppPrev=&pWInfo->pLoops, p=*ppPrev; p; ppPrev=&p->pNextLoop, p=*ppPrev){

    }
    if( (p->prereq & pTemplate->prereq)==p->prereq
     && p->rSetup<=pTemplate->rSetup
     && p->rRun<=pTemplate->rRun
    ){
      /* Already holding an equal or better WhereLoop.
      ** Return without changing or adding anything */
      goto whereLoopInsert_noop;
    }
    if( (p->prereq & pTemplate->prereq)==pTemplate->prereq
     && p->rSetup>=pTemplate->rSetup
     && p->rRun>=pTemplate->rRun
    ){
      /* Overwrite an existing WhereLoop with a better one */
      pNext = p->pNextLoop;
      whereLoopClear(db, p);
      break;
    }
  }

  /* If we reach this point it means that either p[] should be overwritten
  ** with pTemplate[] if p[] exists, or if p==NULL then allocate a new
  ** WhereLoop and insert it.
  */
#if WHERETRACE_ENABLED
  if( sqlite3WhereTrace & 0x8 ){
    if( p!=0 ){
      sqlite3DebugPrintf("ins-del:  ");
      whereLoopPrint(p, pBuilder->pTabList);
    }
    sqlite3DebugPrintf("ins-new:  ");
    whereLoopPrint(pTemplate, pBuilder->pTabList);
  }
#endif
  if( p==0 ){
    p = pToFree = sqlite3DbMallocRaw(db, sizeof(WhereLoop));
    if( p==0 ) return SQLITE_NOMEM;
  }
  if( pTemplate->nTerm ){
    paTerm = sqlite3DbMallocRaw(db, pTemplate->nTerm*sizeof(p->aTerm[0]));
    if( paTerm==0 ){

    if( pIndex && pIndex->tnum==0 ){
      p->u.btree.pIndex = 0;
    }
  }else{
    pTemplate->u.vtab.needFree = 0;
  }
  return SQLITE_OK;

  /* Jump here if the insert is a no-op */
whereLoopInsert_noop:
#if WHERETRACE_ENABLED
  if( sqlite3WhereTrace & 0x8 ){
    sqlite3DebugPrintf("ins-noop: ");
    whereLoopPrint(pTemplate, pBuilder->pTabList);
  }
#endif
  return SQLITE_OK;  
}

/*
** We have so far matched pBuilder->pNew->u.btree.nEq terms of the index pIndex.
** Try to match one more.
**
** If pProbe->tnum==0, that means pIndex is a fake index used for the

    WhereTerm *pWCEnd = pWC->a + pWC->nTerm;
    for(pTerm=pWC->a; rc==SQLITE_OK && pTerm<pWCEnd; pTerm++){
      if( termCanDriveIndex(pTerm, pSrc, 0) ){
        pNew->u.btree.nEq = 1;
        pNew->u.btree.pIndex = 0;
        pNew->nTerm = 1;
        pNew->aTerm[0] = pTerm;
        pNew->rSetup = 20*rLogSize*pSrc->pTab->nRowEst;
        pNew->nOut = (double)10;
        pNew->rRun = rLogSize + pNew->nOut;
        pNew->wsFlags = WHERE_TEMP_INDEX;
        pNew->prereq = mExtra | pTerm->prereqRight;
        rc = whereLoopInsert(pBuilder, pNew);
      }
    }

        for(jj=0, pTo=aTo; jj<nTo; jj++, pTo++){
          if( pTo->maskLoop==maskNew && pTo->isOrderedValid==isOrderedValid ){
            break;
          }
        }
        if( jj>=nTo ){
          if( nTo>=mxChoice && rCost>=mxCost ){
#ifdef WHERETRACE_ENABLED
            if( sqlite3WhereTrace&0x4 ){
              sqlite3DebugPrintf("Skip   %s cost=%-7.2g order=%c\n",
                  wherePathName(pFrom, iLoop, pWLoop), rCost,
                  isOrderedValid ? (isOrdered ? 'Y' : 'N') : '?');
            }
#endif
            continue;
          }
          /* Add a new Path to the aTo[] set */
          if( nTo<mxChoice ){
            /* Increase the size of the aTo set by one */
            jj = nTo++;
          }else{
            /* New path replaces the prior worst to keep count below mxChoice */
            for(jj=nTo-1; aTo[jj].rCost<mxCost; jj--){ assert(jj>0); }
          }
          pTo = &aTo[jj];
#ifdef WHERETRACE_ENABLED
          if( sqlite3WhereTrace&0x4 ){
            sqlite3DebugPrintf("New    %s cost=%-7.2g order=%c\n",
                wherePathName(pFrom, iLoop, pWLoop), rCost,
                isOrderedValid ? (isOrdered ? 'Y' : 'N') : '?');
          }
#endif
        }else{
          if( pTo->rCost<=rCost ){
#ifdef WHERETRACE_ENABLED
            if( sqlite3WhereTrace&0x4 ){
              sqlite3DebugPrintf(
                  "Skip   %s cost=%-7.2g order=%c",
                  wherePathName(pFrom, iLoop, pWLoop), rCost,
                  isOrderedValid ? (isOrdered ? 'Y' : 'N') : '?');
              sqlite3DebugPrintf("   vs %s cost=%-7.2g order=%c\n",
                  wherePathName(pTo, iLoop+1, 0), pTo->rCost,
                  pTo->isOrderedValid ? (pTo->isOrdered ? 'Y' : 'N') : '?');
            }
#endif
            continue;
          }
          /* A new and better score for a previously created equivalent path */
#ifdef WHERETRACE_ENABLED
          if( sqlite3WhereTrace&0x4 ){
            sqlite3DebugPrintf(
                "Update %s cost=%-7.2g order=%c",
                wherePathName(pFrom, iLoop, pWLoop), rCost,
                isOrderedValid ? (isOrdered ? 'Y' : 'N') : '?');
            sqlite3DebugPrintf("  was %s cost=%-7.2g order=%c\n",
                wherePathName(pTo, iLoop+1, 0), pTo->rCost,
                pTo->isOrderedValid ? (pTo->isOrdered ? 'Y' : 'N') : '?');

    if( (pLoop->wsFlags & WHERE_TEMP_INDEX)!=0 ){
      constructAutomaticIndex(pParse, sWBI.pWC, pTabItem, notReady, pLevel);
    }else
#endif
    if( pLoop->u.btree.pIndex!=0 ){
      Index *pIx = pLoop->u.btree.pIndex;
      KeyInfo *pKey = sqlite3IndexKeyinfo(pParse, pIx);

      /* FIXME:  As an optimization use pTabItem->iCursor if WHERE_IDX_ONLY */
      int iIndexCur = pLevel->iIdxCur = iIdxCur ? iIdxCur : pParse->nTab++;
      assert( pIx->pSchema==pTab->pSchema );
      assert( iIndexCur>=0 );
      sqlite3VdbeAddOp4(v, OP_OpenRead, iIndexCur, pIx->tnum, iDb,
                        (char*)pKey, P4_KEYINFO_HANDOFF);
      VdbeComment((v, "%s", pIx->zName));
    }
    sqlite3CodeVerifySchema(pParse, iDb);

# it appends the ::sqlite_query_plan variable.
#
proc queryplan {sql} {
  set ::sqlite_sort_count 0
  set data [execsql $sql]
  if {$::sqlite_sort_count} {set x sort} {set x nosort}
  lappend data $x
  set eqp [execsql "EXPLAIN QUERY PLAN $sql"]
  # puts eqp=$eqp
  foreach {a b c x} $eqp {
    if {[regexp { TABLE (\w+ AS )?(\w+) USING.* INDEX (\w+)\W} \
        $x all as tab idx]} {
      lappend data $tab $idx
    } elseif {[regexp { TABLE (\w+ AS )?(\w+)\W} $x all as tab]} {
      lappend data $tab *
    }
  }
  return $data   
  # return [concat $data $::sqlite_query_plan]
}


# Prefer a UNIQUE index over another index.
#
do_test where2-1.1 {
  queryplan {