SQLite

      if( pzBuffer ){
        *pzBuffer = zAlloc;
      }
    }else{
      if( ExprHasProperty(p, EP_Reduced|EP_TokenOnly) ){
        pNew->pWin = 0;
      }else{
        pNew->pWin = sqlite3WindowDup(db, p->pWin);
      }
      if( !ExprHasProperty(p, EP_TokenOnly|EP_Leaf) ){
        if( pNew->op==TK_SELECT_COLUMN ){
          pNew->pLeft = p->pLeft;
          assert( p->iColumn==0 || p->pRight==0 );
          assert( p->pRight==0  || p->pRight==p->pLeft );
        }else{

          sqlite3WindowUpdate(pParse, pSel->pWinDefn, pExpr->pWin, pDef);
          if( 0==pSel->pWin 
           || 0==sqlite3WindowCompare(pParse, pSel->pWin, pExpr->pWin) 
          ){
            pExpr->pWin->pNextWin = pSel->pWin;
            pSel->pWin = pExpr->pWin;
          }
          pExpr->pWin->pFunc = pDef;
          pExpr->pWin->nArg = (pExpr->x.pList ? pExpr->x.pList->nExpr : 0);
        }else{
          NameContext *pNC2 = pNC;
          pExpr->op = TK_AGG_FUNCTION;
          pExpr->op2 = 0;
          while( pNC2 && !sqlite3FunctionUsesThisSrc(pExpr, pNC2->pSrcList) ){
            pExpr->op2++;
            pNC2 = pNC2->pNext;

  Expr *pStart;           /* Expression for "<expr> PRECEDING" */
  Expr *pEnd;             /* Expression for "<expr> FOLLOWING" */

  Window *pNextWin;       /* Next window function belonging to this SELECT */

  Expr *pFilter;
  FuncDef *pFunc;
  int nArg;

  int iEphCsr;            /* Temp table used by this window */
  int regAccum;
  int regResult;

  int csrApp;             /* Function cursor (used by min/max) */
  int regApp;             /* Function register (also used by min/max) */

void sqlite3WindowAttach(Parse*, Expr*, Window*);
int sqlite3WindowCompare(Parse*, Window*, Window*);
void sqlite3WindowCodeInit(Parse*, Window*);
void sqlite3WindowCodeStep(Parse*, Select*, WhereInfo*, int, int);
int sqlite3WindowRewrite(Parse*, Select*);
int sqlite3ExpandSubquery(Parse*, struct SrcList_item*);
void sqlite3WindowUpdate(Parse*, Window*, Window*, FuncDef*);
Window *sqlite3WindowDup(sqlite3 *db, Window *p);

/*
** Assuming zIn points to the first byte of a UTF-8 character,
** advance zIn to point to the first byte of the next UTF-8 character.
*/
#define SQLITE_SKIP_UTF8(zIn) {                        \
  if( (*(zIn++))>=0xc0 ){                              \

  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
  i64 *p = (i64*)sqlite3_aggregate_context(pCtx, sizeof(*p));
  if( p ) (*p)++;
}
static void row_numberInverseFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
}
static void row_numberValueFunc(sqlite3_context *pCtx){
  i64 *p = (i64*)sqlite3_aggregate_context(pCtx, sizeof(*p));
  sqlite3_result_int64(pCtx, (p ? *p : 0));
}

/*
** Context object type used by rank() and dense_rank().

*/
struct CallCount {
  i64 nValue;
  i64 nStep;
  i64 nTotal;
};

/*
** Implementation of built-in window function dense_rank().
*/
static void dense_rankStepFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
  struct CallCount *p;
  p = (struct CallCount*)sqlite3_aggregate_context(pCtx, sizeof(*p));
  if( p ) p->nStep = 1;
}
static void dense_rankInverseFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
}
static void dense_rankValueFunc(sqlite3_context *pCtx){
  struct CallCount *p;

  if( p ){
    p->nStep++;
    if( p->nValue==0 ){
      p->nValue = p->nStep;
    }
  }
}
static void rankInverseFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
}
static void rankValueFunc(sqlite3_context *pCtx){
  struct CallCount *p;

    }
    p->nStep++;
    if( p->nValue==0 ){
      p->nValue = p->nStep;
    }
  }
}
static void percent_rankInverseFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
}
static void percent_rankValueFunc(sqlite3_context *pCtx){
  struct CallCount *p;

  if( p ){
    if( p->nTotal==0 ){
      p->nTotal = sqlite3_value_int64(apArg[0]);
    }
    p->nStep++;
  }
}
static void cume_distInverseFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
}
static void cume_distValueFunc(sqlite3_context *pCtx){
  struct CallCount *p;
  p = (struct CallCount*)sqlite3_aggregate_context(pCtx, sizeof(*p));
  if( p ){
    double r = (double)(p->nStep) / (double)(p->nTotal);
    sqlite3_result_double(pCtx, r);
  }
}




struct NtileCtx {
  i64 nTotal;                     /* Total rows in partition */
  i64 nParam;                     /* Parameter passed to ntile(N) */
  i64 iRow;                       /* Current row */
};

/*

            pCtx, "argument of ntile must be a positive integer", -1
        );
      }
    }
    p->iRow++;
  }
}
static void ntileInverseFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
}
static void ntileValueFunc(sqlite3_context *pCtx){
  struct NtileCtx *p;

      }else{
        sqlite3_result_int64(pCtx, 1 + nLarge + (iRow-iSmall)/nSize);
      }
    }
  }
}




struct LastValueCtx {
  sqlite3_value *pVal;
  int nVal;
};

/*
** Implementation of last_value().

  p = (struct LastValueCtx *)sqlite3_aggregate_context(pCtx, sizeof(*p));
  if( p ){
    sqlite3_value_free(p->pVal);
    p->pVal = sqlite3_value_dup(apArg[0]);
    p->nVal++;
  }
}
static void last_valueInverseFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
  struct LastValueCtx *p;
  p = (struct LastValueCtx *)sqlite3_aggregate_context(pCtx, sizeof(*p));
  if( p ){

  if( p && p->pVal ){
    sqlite3_result_value(pCtx, p->pVal);
    sqlite3_value_free(p->pVal);
    p->pVal = 0;
  }
}





static void nth_valueStepFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
}
static void nth_valueInverseFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
}
static void nth_valueValueFunc(sqlite3_context *pCtx){
}

static void first_valueStepFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
}
static void first_valueInverseFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
}
static void first_valueValueFunc(sqlite3_context *pCtx){
}

static void leadStepFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
}
static void leadInverseFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
}
static void leadValueFunc(sqlite3_context *pCtx){
}

static void lagStepFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
}
static void lagInverseFunc(
  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
}
static void lagValueFunc(sqlite3_context *pCtx){
}

#define WINDOWFUNC(name,nArg,extra) {                                      \
  nArg, (SQLITE_UTF8|SQLITE_FUNC_WINDOW|extra), 0, 0,                      \
  name ## StepFunc, name ## ValueFunc, name ## ValueFunc,                  \
  name ## InverseFunc, #name                                               \
}

#define WINDOWFUNCF(name,nArg,extra) {                                     \
  nArg, (SQLITE_UTF8|SQLITE_FUNC_WINDOW|extra), 0, 0,                      \
  name ## StepFunc, name ## FinalizeFunc, name ## ValueFunc,               \
  name ## InverseFunc, #name                                               \
}

/*
** Register those built-in window functions that are not also aggregates.
*/
void sqlite3WindowFunctions(void){
  static FuncDef aWindowFuncs[] = {

      sqlite3ExprDelete(db, pWin->pEnd);
      pWin->pStart = pWin->pEnd = 0;
      pWin->eType = TK_RANGE;
      pWin->eStart = TK_UNBOUNDED;
      pWin->eEnd = TK_CURRENT;
    }
  }

}

typedef struct WindowRewrite WindowRewrite;
struct WindowRewrite {
  Window *pWin;
  ExprList *pSub;
};

    case TK_FUNCTION:
      if( pExpr->pWin==0 ){
        break;
      }else{
        Window *pWin;
        for(pWin=p->pWin; pWin; pWin=pWin->pNextWin){
          if( pExpr->pWin==pWin ){
            pExpr->pWin->pOwner = pExpr;
            return WRC_Prune;
          }
        }
      }
      /* Fall through.  */

    case TK_COLUMN: {

  return pWin;
}

void sqlite3WindowAttach(Parse *pParse, Expr *p, Window *pWin){
  if( p ){
    p->pWin = pWin;

  }else{
    sqlite3WindowDelete(pParse->db, pWin);
  }
}

/*
** Return 0 if the two window objects are identical, or non-zero otherwise.

  sqlite3VdbeAddOp2(v, OP_Integer, 0, regZero);
  sqlite3VdbeAddOp2(v, OP_MustBeInt, reg, sqlite3VdbeCurrentAddr(v)+2);
  sqlite3VdbeAddOp3(v, OP_Ge, regZero, sqlite3VdbeCurrentAddr(v)+2, reg);
  sqlite3VdbeAddOp2(v, OP_Halt, SQLITE_ERROR, OE_Abort);
  sqlite3VdbeAppendP4(v, (void*)azErr[bEnd], P4_STATIC);
}






/*
** Generate VM code to invoke either xStep() (if bInverse is 0) or 
** xInverse (if bInverse is non-zero) for each window function in the 
** linked list starting at pMWin.
*/
static void windowAggStep(
  Parse *pParse, 
  Window *pMWin, 
  int csr,
  int bInverse, 
  int reg,
  int regPartSize                 /* Register containing size of partition */
){
  Vdbe *v = sqlite3GetVdbe(pParse);
  Window *pWin;
  for(pWin=pMWin; pWin; pWin=pWin->pNextWin){
    int flags = pWin->pFunc->funcFlags;
    int regArg;
    int nArg = pWin->nArg;

    if( csr>=0 ){
      int i;
      for(i=0; i<pWin->nArg; i++){
        sqlite3VdbeAddOp3(v, OP_Column, csr, pWin->iArgCol+i, reg+i);
      }
      regArg = reg;
      if( flags & SQLITE_FUNC_WINDOW_SIZE ){
        if( nArg==0 ){
          regArg = regPartSize;
        }else{

           || pWin->pFunc->xSFunc==lagStepFunc 
    ){
      /* no-op */
    }else{
      int addrIf = 0;
      if( pWin->pFilter ){
        int regTmp;

        if( csr>0 ){
          regTmp = sqlite3GetTempReg(pParse);
          sqlite3VdbeAddOp3(v, OP_Column, csr, pWin->iArgCol+pWin->nArg,regTmp);
        }else{
          regTmp = regArg + pWin->nArg;
        }
        addrIf = sqlite3VdbeAddOp3(v, OP_IfNot, regTmp, 0, 1);
        if( csr>0 ){
          sqlite3ReleaseTempReg(pParse, regTmp);
        }
      }
      if( pWin->pFunc->funcFlags & SQLITE_FUNC_NEEDCOLL ){

        sqlite3VdbeAddOp1(v, OP_ResetSorter, pWin->csrApp);
      }
    }else if( pWin->regApp ){
    }else{
      if( bFinal==0 ){
        sqlite3VdbeAddOp2(v, OP_Null, 0, pWin->regResult);
      }
      sqlite3VdbeAddOp2(v, OP_AggFinal, pWin->regAccum, pWin->nArg);
      sqlite3VdbeAppendP4(v, pWin->pFunc, P4_FUNCDEF);
      if( bFinal ){
        sqlite3VdbeAddOp2(v, OP_Copy, pWin->regAccum, pWin->regResult);
        sqlite3VdbeAddOp2(v, OP_Null, 0, pWin->regAccum);
      }else{
        sqlite3VdbeChangeP3(v, -1, pWin->regResult);
      }

      sqlite3VdbeAddOp3(v, OP_Gt, pWin->regApp+1, lbl, tmpReg);
      sqlite3VdbeAddOp3(v, OP_SeekRowid, csr, lbl, tmpReg);
      sqlite3VdbeAddOp3(v, OP_Column, csr, pWin->iArgCol, pWin->regResult);
      sqlite3VdbeResolveLabel(v, lbl);
      sqlite3ReleaseTempReg(pParse, tmpReg);
    }
    else if( pFunc->xSFunc==leadStepFunc || pFunc->xSFunc==lagStepFunc ){

      int iEph = pWin->iEphCsr;
      int csr = pWin->csrApp;
      int lbl = sqlite3VdbeMakeLabel(v);
      int tmpReg = sqlite3GetTempReg(pParse);

      if( pWin->nArg<3 ){
        sqlite3VdbeAddOp2(v, OP_Null, 0, pWin->regResult);
      }else{
        sqlite3VdbeAddOp3(v, OP_Column, iEph, pWin->iArgCol+2, pWin->regResult);
      }
      sqlite3VdbeAddOp2(v, OP_Rowid, iEph, tmpReg);
      if( pWin->nArg<2 ){
        int val = (pFunc->xSFunc==leadStepFunc ? 1 : -1);
        sqlite3VdbeAddOp2(v, OP_AddImm, tmpReg, val);
      }else{
        int op = (pFunc->xSFunc==leadStepFunc ? OP_Add : OP_Subtract);
        int tmpReg2 = sqlite3GetTempReg(pParse);
        sqlite3VdbeAddOp3(v, OP_Column, iEph, pWin->iArgCol+1, tmpReg2);
        sqlite3VdbeAddOp3(v, op, tmpReg2, tmpReg, tmpReg);

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);
    nArg = MAX(nArg, pWin->nArg);
    if( pWin->pFunc->xSFunc==nth_valueStepFunc
     || pWin->pFunc->xSFunc==first_valueStepFunc 
    ){
      sqlite3VdbeAddOp2(v, OP_Integer, 0, pWin->regApp);
      sqlite3VdbeAddOp2(v, OP_Integer, 0, pWin->regApp+1);
    }
  }

  windowAggFinal(pParse, pMWin, 1);
  sqlite3VdbeAddOp2(v, OP_Rewind, pMWin->iEphCsr,sqlite3VdbeCurrentAddr(v)+3);
  sqlite3VdbeAddOp2(v, OP_Gosub, regGosub, addrGosub);
  sqlite3VdbeAddOp2(v, OP_Next, pMWin->iEphCsr, sqlite3VdbeCurrentAddr(v)-1);
}

Window *sqlite3WindowDup(sqlite3 *db, Window *p){
  Window *pNew = 0;
  if( p ){
    pNew = sqlite3DbMallocZero(db, sizeof(Window));
    if( pNew ){
      pNew->pFilter = sqlite3ExprDup(db, p->pFilter, 0);
      pNew->pPartition = sqlite3ExprListDup(db, p->pPartition, 0);
      pNew->pOrderBy = sqlite3ExprListDup(db, p->pOrderBy, 0);
      pNew->eType = p->eType;
      pNew->eEnd = p->eEnd;
      pNew->eStart = p->eStart;
      pNew->pStart = sqlite3ExprDup(db, pNew->pStart, 0);
      pNew->pEnd = sqlite3ExprDup(db, pNew->pEnd, 0);

    }
  }
  return pNew;
}

/*
** RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
**
**   As above, except take no action for a "new peer". Invoke
**   the sub-routine once only for each partition.
**
** RANGE BETWEEN CURRENT ROW AND CURRENT ROW
**
**   As above, except that the "new peer" condition is handled in the
**   same way as "new partition" (so there is no "else if" block).
**
** RANGE BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING
**
**   One way is to just reverse the sort order and do as for BETWEEN 
**   UNBOUNDED PRECEDING AND CURRENT ROW. But that is not quite the same for
**   things like group_concat(). And perhaps other user defined aggregates 
**   as well.
**
**   ...
**     if( new partition ){
**       Gosub flush_partition;
**       ResetSorter eph-table
**     }
**     AggStep
**     Insert (record into eph-table)
**   sqlite3WhereEnd()
**   Gosub flush_partition
**
**  flush_partition:
**   OpenDup (csr -> csr2)
**   foreach (record in eph-table) {
**     if( new peer ){
**       while( csr2!=csr ){
**         AggStep (xInverse)
**         Next (csr2)
**       }
**     }
**     AggFinal (xValue)


**     Gosub addrGosub
**   }
**
**========================================================================
**
** ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
**   ...
**     if( new partition ){
**       AggFinal (xFinalize)
**     }
**     AggStep
**     AggFinal (xValue)
**     Gosub addrGosub
**   sqlite3WhereEnd()
**
*/
void sqlite3WindowCodeStep(
  Parse *pParse, 
  Select *p,
  WhereInfo *pWInfo,
  int regGosub, 
  int addrGosub
){
  Window *pMWin = p->pWin;
  Window *pWin;

  /*
  ** Call windowCodeRowExprStep() for all window modes *except*:
  **
  **   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
  */
  if( (pMWin->eType==TK_ROWS 
   && (pMWin->eStart!=TK_UNBOUNDED||pMWin->eEnd!=TK_CURRENT||!pMWin->pOrderBy))
   || (pMWin->eStart==TK_CURRENT&&pMWin->eEnd==TK_UNBOUNDED&&pMWin->pOrderBy)
  ){
    windowCodeRowExprStep(pParse, p, pWInfo, regGosub, addrGosub);
    return;
  }

  /*
  ** Call windowCodeCacheStep() if there is a window function that requires
  ** that the entire partition be cached in a temp table before any rows
  ** are returned.
  */
  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)
    ){
      windowCodeCacheStep(pParse, p, pWInfo, regGosub, addrGosub);
      return;
    }
  }


  windowCodeDefaultStep(pParse, p, pWInfo, regGosub, addrGosub);
}