SQLite

  Expr *pFilter;          /* The FILTER expression */
  FuncDef *pFunc;         /* The function */
  int iEphCsr;            /* Partition buffer or Peer buffer */
  int regAccum;
  int regResult;
  int csrApp;             /* Function cursor (used by min/max) */
  int regApp;             /* Function register (also used by min/max) */
  int regPart;            /* First in a set of registers holding PARTITION BY
  int regPart;            /* Array of registers for PARTITION BY values */
                          ** and ORDER BY values for the window */
  Expr *pOwner;           /* Expression object this window is attached to */
  int nBufferCol;         /* Number of columns in buffer table */
  int iArgCol;            /* Offset of first argument for this function */
  int regFirst;
};

#ifndef SQLITE_OMIT_WINDOWFUNC

** This is called by code in select.c before it calls sqlite3WhereBegin()
** to begin iterating through the sub-query results. It is used to allocate
** and initialize registers and cursors used by sqlite3WindowCodeStep().
*/
void sqlite3WindowCodeInit(Parse *pParse, Window *pMWin){
  Window *pWin;
  Vdbe *v = sqlite3GetVdbe(pParse);
  int nPart = (pMWin->pPartition ? pMWin->pPartition->nExpr : 0);
  nPart += (pMWin->pOrderBy ? pMWin->pOrderBy->nExpr : 0);
  if( nPart ){

  /* Allocate registers to use for PARTITION BY values, if any. Initialize
  ** said registers to NULL.  */
  if( pMWin->pPartition ){
    int nExpr = pMWin->pPartition->nExpr;
    pMWin->regPart = pParse->nMem+1;
    pParse->nMem += nPart;
    sqlite3VdbeAddOp3(v, OP_Null, 0, pMWin->regPart, pMWin->regPart+nPart-1);
    pParse->nMem += nExpr;
    sqlite3VdbeAddOp3(v, OP_Null, 0, pMWin->regPart, pMWin->regPart+nExpr-1);
  }

  pMWin->regFirst = ++pParse->nMem;
  sqlite3VdbeAddOp2(v, OP_Integer, 1, pMWin->regFirst);

  for(pWin=pMWin; pWin; pWin=pWin->pNextWin){
    FuncDef *p = pWin->pFunc;

**         }
**         RETURN_ROW
**       }
**       while( !eof csrCurrent ){
**         RETURN_ROW
**       }
**
** The text above leaves out many details. Refer to the code and comments
** below for a more complete picture.
*/
void sqlite3WindowCodeStep(
  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 */

    sqlite3VdbeAddOp3(v, OP_Copy, regPeer, s.current.reg, pOrderBy->nExpr-1);
    sqlite3VdbeAddOp3(v, OP_Copy, regPeer, s.end.reg, pOrderBy->nExpr-1);
  }

  sqlite3VdbeAddOp2(v, OP_Integer, 0, pMWin->regFirst);
  sqlite3VdbeAddOp2(v, OP_Goto, 0, lblWhereEnd);

  /* Begin generating SECOND_ROW_CODE */
  VdbeModuleComment((pParse->pVdbe, "Begin WindowCodeStep.SECOND_ROW"));
  sqlite3VdbeJumpHere(v, addrIfNot);
  if( regPeer ){
    windowIfNewPeer(pParse, pOrderBy, regNewPeer, regPeer, lblWhereEnd);
  }
  if( pMWin->eStart==TK_FOLLOWING ){
    windowCodeOp(&s, WINDOW_AGGSTEP, 0, 0);
    if( pMWin->eEnd!=TK_UNBOUNDED ){

        if( regEnd ) addr = sqlite3VdbeAddOp3(v, OP_IfPos, regEnd, 0, 1);
        windowCodeOp(&s, WINDOW_RETURN_ROW, 0, 0);
        windowCodeOp(&s, WINDOW_AGGINVERSE, regStart, 0);
        if( regEnd ) sqlite3VdbeJumpHere(v, addr);
      }
    }
  }
  VdbeModuleComment((pParse->pVdbe, "End WindowCodeStep.SECOND_ROW"));

  /* End of the main input loop */
  sqlite3VdbeResolveLabel(v, lblWhereEnd);
  sqlite3WhereEnd(pWInfo);

  /* Fall through */
  if( pMWin->pPartition ){
    addrInteger = sqlite3VdbeAddOp2(v, OP_Integer, 0, regFlushPart);
    sqlite3VdbeJumpHere(v, addrGosubFlush);
  }

  VdbeModuleComment((pParse->pVdbe, "Begin WindowCodeStep.FLUSH"));
  addrEmpty = sqlite3VdbeAddOp1(v, OP_Rewind, csrWrite);
  if( pMWin->eEnd==TK_PRECEDING ){
    windowCodeOp(&s, WINDOW_AGGSTEP, regEnd, 0);
    windowCodeOp(&s, WINDOW_RETURN_ROW, 0, 0);
  }else if( pMWin->eStart==TK_FOLLOWING ){
    int addrStart;
    int addrBreak1;

    sqlite3VdbeAddOp2(v, OP_Goto, 0, addrStart);
    sqlite3VdbeJumpHere(v, addrBreak);
  }
  sqlite3VdbeJumpHere(v, addrEmpty);

  sqlite3VdbeAddOp1(v, OP_ResetSorter, s.current.csr);
  sqlite3VdbeAddOp2(v, OP_Integer, 1, pMWin->regFirst);
  VdbeModuleComment((pParse->pVdbe, "End WindowCodeStep.FLUSH"));
  if( pMWin->pPartition ){
    sqlite3VdbeChangeP1(v, addrInteger, sqlite3VdbeCurrentAddr(v));
    sqlite3VdbeAddOp1(v, OP_Return, regFlushPart);
  }
}

#endif /* SQLITE_OMIT_WINDOWFUNC */