SQLite

  WhereClause *pWC = p->pWC;      /* The WHERE clause */
  struct SrcList_item *pSrc = p->pSrc; /* The FROM clause term to search */
  Table *pTab = pSrc->pTab;
  sqlite3_index_info *pIdxInfo;
  struct sqlite3_index_constraint *pIdxCons;
  struct sqlite3_index_constraint_usage *pUsage;
  WhereTerm *pTerm;
  int i, j;
  int i, j, k;
  int nOrderBy;
  int sortOrder;                  /* Sort order for IN clauses */
  int bAllowIN;                   /* Allow IN optimizations */
  double rCost;

  /* Make sure wsFlags is initialized to some sane value. Otherwise, if the 
  ** malloc in allocateIndexInfo() fails and this function returns leaving
  ** wsFlags in an uninitialized state, the caller may behave unpredictably.
  */

      pIdxInfo->nOrderBy = 0;
    }
  
    if( vtabBestIndex(pParse, pTab, pIdxInfo) ){
      return;
    }
  
    sortOrder = SQLITE_SO_ASC;
    pIdxCons = *(struct sqlite3_index_constraint**)&pIdxInfo->aConstraint;
    for(i=0; i<pIdxInfo->nConstraint; i++, pIdxCons++){
      if( pUsage[i].argvIndex>0 ){
        j = pIdxCons->iTermOffset;
        pTerm = &pWC->a[j];
        p->cost.used |= pTerm->prereqRight;
        if( (pTerm->eOperator & WO_IN)!=0 && pUsage[i].omit==0 ){
          /* Do not attempt to use an IN constraint if the virtual table
          ** says that the equivalent EQ constraint cannot be safely omitted.
          ** If we do attempt to use such a constraint, some rows might be
          ** repeated in the output. */
          break;
        if( (pTerm->eOperator & WO_IN)!=0 ){
          if( pUsage[i].omit==0 ){
            /* Do not attempt to use an IN constraint if the virtual table
            ** says that the equivalent EQ constraint cannot be safely omitted.
            ** If we do attempt to use such a constraint, some rows might be
            ** repeated in the output. */
            break;
          }
          for(k=0; k<pIdxInfo->nOrderBy; k++){
            if( pIdxInfo->aOrderBy[k].iColumn==pIdxCons->iColumn ){
              sortOrder = pIdxInfo->aOrderBy[k].desc;
              break;
            }
          }
        }
      }
    }
    if( i>=pIdxInfo->nConstraint ) break;
  }
  
  /* If there is an ORDER BY clause, and the selected virtual table index

  if( (SQLITE_BIG_DBL/((double)2))<rCost ){
    p->cost.rCost = (SQLITE_BIG_DBL/((double)2));
  }else{
    p->cost.rCost = rCost;
  }
  p->cost.plan.u.pVtabIdx = pIdxInfo;
  if( pIdxInfo->orderByConsumed ){
    assert( sortOrder==0 || sortOrder==1 );
    p->cost.plan.wsFlags |= WHERE_ORDERED;
    p->cost.plan.wsFlags |= WHERE_ORDERED + sortOrder*WHERE_REVERSE;
    p->cost.plan.nOBSat = nOrderBy;
  }else{
    p->cost.plan.nOBSat = p->i ? p->aLevel[p->i-1].plan.nOBSat : 0;
  }
  p->cost.plan.nEq = 0;
  pIdxInfo->nOrderBy = nOrderBy;