SQLite

  if( regInvArg ){
    windowAggStep(pParse, pMWin, pMWin->iEphCsr, 1, regInvArg, regInvSize);
  }
  sqlite3VdbeAddOp2(v, OP_Next, pMWin->iEphCsr, addr);
  sqlite3VdbeJumpHere(v, addr+1);   /* The OP_Goto */
}

/*
** Generate code to set the accumulator register for each window function
** in the linked list passed as the second argument to NULL. And perform
** any equivalent initialization required by any built-in window functions
** in the list.
*/
static int windowInitAccum(Parse *pParse, Window *pMWin){
  Vdbe *v = sqlite3GetVdbe(pParse);
  int regArg;
  int nArg = 0;
  Window *pWin;
  for(pWin=pMWin; pWin; pWin=pWin->pNextWin){
    sqlite3VdbeAddOp2(v, OP_Null, 0, pWin->regAccum);

  regArg = pParse->nMem+1;
  pParse->nMem += nArg;
  return regArg;
}


/*
** This function does the work of sqlite3WindowCodeStep() for all "ROWS"
** window frame types except for "BETWEEN UNBOUNDED PRECEDING AND CURRENT


** ROW". Pseudo-code for each follows.


**


** ROWS BETWEEN <expr1> PRECEDING AND <expr2> FOLLOWING
**
**     ...
**       if( new partition ){
**         Gosub flush_partition
**       }
**       Insert (record in eph-table)
**     sqlite3WhereEnd()

  sqlite3VdbeAddOp1(v, OP_Return, regFlushPart);

  /* Jump to here to skip over flush_partition */
  sqlite3VdbeJumpHere(v, addrGoto);
}

/*
** This function does the work of sqlite3WindowCodeStep() for cases that
** would normally be handled by windowCodeDefaultStep() when there are
** one or more built-in window-functions that require the entire partition
** to be cached in a temp table before any rows can be returned. Additionally.
** "RANGE BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING" is always handled by
** this function.
**
** Pseudo-code corresponding to the VM code generated by this function
** for each type of window follows.
**
** RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
**
**   flush_partition:
**     Once {
**       OpenDup (iEphCsr -> csrLead)
**     }
**     Integer ctr 0

**       Next iEphCsr
**     }
**
**     ResetSorter (csr)
**     Return
**
** ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
**
**   As above, except that the "if( new peer )" branch is always taken.
**
** RANGE BETWEEN CURRENT ROW AND CURRENT ROW 
**
**   As above, except that each of the for() loops becomes:
**
**         for(i=0; i<ctr; i++){
**           Gosub addrGosub
**           AggStep (xInverse, iEphCsr)
**           Next iEphCsr
**         }
**
** RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
**
**   flush_partition:
**     Once {
**       OpenDup (iEphCsr -> csrLead)
**     }
**     foreach row (csrLead) {
**       AggStep (csrLead)
**     }
**     foreach row (iEphCsr) {
**       Gosub addrGosub
**     }
** 
** RANGE BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING
**
**   flush_partition:
**     Once {
**       OpenDup (iEphCsr -> csrLead)
**     }
**     foreach row (csrLead){
**       AggStep (csrLead)
**     }
**     Rewind (csrLead)
**     Integer ctr 0
**     foreach row (csrLead){
**       if( new peer ){
**         AggFinal (xValue)
**         for(i=0; i<ctr; i++){
**           Gosub addrGosub
**           AggStep (xInverse, iEphCsr)
**           Next iEphCsr
**         }
**         Integer ctr 0
**       }
**       Incr ctr
**     }
**
**     AggFinal (xFinalize)
**     for(i=0; i<ctr; i++){
**       Gosub addrGosub
**       Next iEphCsr
**     }
**
**     ResetSorter (csr)
**     Return
*/
static void windowCodeCacheStep(
  Parse *pParse, 
  Select *p,
  WhereInfo *pWInfo,
  int regGosub, 
  int addrGosub
){
  Window *pMWin = p->pWin;
  Vdbe *v = sqlite3GetVdbe(pParse);
  Window *pWin;
  int k;
  int addr;
  ExprList *pPart = pMWin->pPartition;
  ExprList *pOrderBy = pMWin->pOrderBy;
  int nPeer = pOrderBy ? pOrderBy->nExpr : 0;
  int regNewPeer;

  int addrGoto;                   /* Address of Goto used to jump flush_par.. */
  int addrNext;                   /* Jump here for next iteration of loop */
  int regFlushPart;
  int lblFlushPart;
  int csrLead;
  int regCtr;
  int regArg;                     /* Register array to martial function args */
  int regSize;
  int nArg;

  int lblEmpty;
  int bReverse = pMWin->pOrderBy && pMWin->eStart==TK_CURRENT 
          && pMWin->eEnd==TK_UNBOUNDED;

  assert( (pMWin->eStart==TK_UNBOUNDED && pMWin->eEnd==TK_CURRENT) 
       || (pMWin->eStart==TK_UNBOUNDED && pMWin->eEnd==TK_UNBOUNDED) 
       || (pMWin->eStart==TK_CURRENT && pMWin->eEnd==TK_CURRENT) 
       || (pMWin->eStart==TK_CURRENT && pMWin->eEnd==TK_UNBOUNDED) 
  );

  lblEmpty = sqlite3VdbeMakeLabel(v);

  regNewPeer = pParse->nMem+1;
  pParse->nMem += nPeer;

  /* Allocate register and label for the "flush_partition" sub-routine. */
  regFlushPart = ++pParse->nMem;
  lblFlushPart = sqlite3VdbeMakeLabel(v);

  Parse *pParse,                  /* Parse context */
  Select *p,                      /* Rewritten SELECT statement */
  WhereInfo *pWInfo,              /* Context returned by sqlite3WhereBegin() */
  int regGosub,                   /* Register for OP_Gosub */
  int addrGosub                   /* OP_Gosub here to return each row */
){
  Window *pMWin = p->pWin;


  /* There are three different functions that may be used to do the work
  ** of this one, depending on the window frame and the specific built-in
  ** window functions used (if any).
  **
  ** windowCodeRowExprStep() handles all "ROWS" window frames, except for:
  **
  **   ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
  **
  ** The exception is because windowCodeRowExprStep() implements all window
  ** frame types by caching the entire partition in a temp table, and
  ** "ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW" is easy enough to
  ** implement without such a cache.
  **
  ** windowCodeCacheStep() is used for:
  **
  **   RANGE BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING
  **
  ** It is also used for anything not handled by windowCodeRowExprStep() 
  ** that invokes a built-in window function that requires the entire 
  ** partition to be cached in a temp table before any rows are returned
  ** (e.g. nth_value() or percent_rank()).
  **
  ** Finally, assuming there is no built-in window function that requires
  ** the partition to be cached, windowCodeDefaultStep() is used for:
  **
  **   RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW 
  **   RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
  **   RANGE BETWEEN CURRENT ROW AND CURRENT ROW 
  **   ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
  **
  ** windowCodeDefaultStep() is the only one of the three functions that
  ** does not cache each partition in a temp table before beginning to
  ** return rows.
  */
  if( pMWin->eType==TK_ROWS 
   && (pMWin->eStart!=TK_UNBOUNDED||pMWin->eEnd!=TK_CURRENT||!pMWin->pOrderBy)
  ){
    windowCodeRowExprStep(pParse, p, pWInfo, regGosub, addrGosub);
  }else{
    Window *pWin;
    int bCache = 0;               /* True to use CacheStep() */

    if( pMWin->eStart==TK_CURRENT && pMWin->eEnd==TK_UNBOUNDED ){
      bCache = 1;
    }else{



      for(pWin=pMWin; pWin; pWin=pWin->pNextWin){
        FuncDef *pFunc = pWin->pFunc;
        if( (pFunc->funcFlags & SQLITE_FUNC_WINDOW_SIZE)
         || (pFunc->xSFunc==nth_valueStepFunc)
         || (pFunc->xSFunc==first_valueStepFunc)
         || (pFunc->xSFunc==leadStepFunc)
         || (pFunc->xSFunc==lagStepFunc)
        ){
          bCache = 1;
          break;
        }
      }
    }

    /* Otherwise, call windowCodeDefaultStep().  */