if( pScan->iEquiv>=pScan->nEquiv ) break;
    pWC = pScan->pOrigWC;
    k = 0;
    pScan->iEquiv++;
  }
  return 0;
}












/*
** Initialize a WHERE clause scanner object.  Return a pointer to the
** first match.  Return NULL if there are no matches.
**
** The scanner will be searching the WHERE clause pWC.  It will look
** for terms of the form "X <op> <expr>" where X is column iColumn of table
................................................................................
  Index *pIdx             /* Must be compatible with this index */
){
  pScan->pOrigWC = pWC;
  pScan->pWC = pWC;
  pScan->pIdxExpr = 0;
  pScan->idxaff = 0;
  pScan->zCollName = 0;





  if( pIdx ){
    int j = iColumn;
    iColumn = pIdx->aiColumn[j];
    if( iColumn==XN_EXPR ){
      pScan->pIdxExpr = pIdx->aColExpr->a[j].pExpr;
      pScan->zCollName = pIdx->azColl[j];
      pScan->idxaff = sqlite3ExprAffinity(pScan->pIdxExpr);

    }else if( iColumn==pIdx->pTable->iPKey ){
      iColumn = XN_ROWID;
    }else if( iColumn>=0 ){
      pScan->idxaff = pIdx->pTable->aCol[iColumn].affinity;
      pScan->zCollName = pIdx->azColl[j];
    }
  }else if( iColumn==XN_EXPR ){
    return 0;
  }
  pScan->opMask = opMask;
  pScan->k = 0;
  pScan->aiCur[0] = iCur;
  pScan->aiColumn[0] = iColumn;
  pScan->nEquiv = 1;
  pScan->iEquiv = 1;
  return whereScanNext(pScan);
}

/*
** Search for a term in the WHERE clause that is of the form "X <op> <expr>"
** where X is a reference to the iColumn of table iCur or of index pIdx
** if pIdx!=0 and <op> is one of the WO_xx operator codes specified by

    if( pScan->iEquiv>=pScan->nEquiv ) break;
    pWC = pScan->pOrigWC;
    k = 0;
    pScan->iEquiv++;
  }
  return 0;
}

/*
** This is whereScanInit() for the case of an index on an expression.
** It is factored out into a separate tail-recursion subroutine so that
** the normal whereScanInit() routine, which is a high-runner, does not
** need to push registers onto the stack as part of its prologue.
*/
static SQLITE_NOINLINE WhereTerm *whereScanInitIndexExpr(WhereScan *pScan){
  pScan->idxaff = sqlite3ExprAffinity(pScan->pIdxExpr);
  return whereScanNext(pScan);
}

/*
** Initialize a WHERE clause scanner object.  Return a pointer to the
** first match.  Return NULL if there are no matches.
**
** The scanner will be searching the WHERE clause pWC.  It will look
** for terms of the form "X <op> <expr>" where X is column iColumn of table
................................................................................
  Index *pIdx             /* Must be compatible with this index */
){
  pScan->pOrigWC = pWC;
  pScan->pWC = pWC;
  pScan->pIdxExpr = 0;
  pScan->idxaff = 0;
  pScan->zCollName = 0;
  pScan->opMask = opMask;
  pScan->k = 0;
  pScan->aiCur[0] = iCur;
  pScan->nEquiv = 1;
  pScan->iEquiv = 1;
  if( pIdx ){
    int j = iColumn;
    iColumn = pIdx->aiColumn[j];
    if( iColumn==XN_EXPR ){
      pScan->pIdxExpr = pIdx->aColExpr->a[j].pExpr;
      pScan->zCollName = pIdx->azColl[j];
      pScan->aiColumn[0] = XN_EXPR;
      return whereScanInitIndexExpr(pScan);
    }else if( iColumn==pIdx->pTable->iPKey ){
      iColumn = XN_ROWID;
    }else if( iColumn>=0 ){
      pScan->idxaff = pIdx->pTable->aCol[iColumn].affinity;
      pScan->zCollName = pIdx->azColl[j];
    }
  }else if( iColumn==XN_EXPR ){
    return 0;
  }



  pScan->aiColumn[0] = iColumn;


  return whereScanNext(pScan);
}

/*
** Search for a term in the WHERE clause that is of the form "X <op> <expr>"
** where X is a reference to the iColumn of table iCur or of index pIdx
** if pIdx!=0 and <op> is one of the WO_xx operator codes specified by