SQLite

  sqlite3_context *pCtx, 
  int nArg,
  sqlite3_value **apArg
){
  i64 *p = (i64*)sqlite3_aggregate_context(pCtx, sizeof(*p));
  if( p ) (*p)++;
}






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(), dense_rank(), percent_rank() and

  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_rankValueFunc(sqlite3_context *pCtx){
  struct CallCount *p;
  p = (struct CallCount*)sqlite3_aggregate_context(pCtx, sizeof(*p));
  if( p ){
    if( p->nStep ){
      p->nValue++;
      p->nStep = 0;

  if( p ){
    p->nStep++;
    if( p->nValue==0 ){
      p->nValue = p->nStep;
    }
  }
}






static void rankValueFunc(sqlite3_context *pCtx){
  struct CallCount *p;
  p = (struct CallCount*)sqlite3_aggregate_context(pCtx, sizeof(*p));
  if( p ){
    sqlite3_result_int64(pCtx, p->nValue);
    p->nValue = 0;
  }

    }
    p->nStep++;
    if( p->nValue==0 ){
      p->nValue = p->nStep;
    }
  }
}






static void percent_rankValueFunc(sqlite3_context *pCtx){
  struct CallCount *p;
  p = (struct CallCount*)sqlite3_aggregate_context(pCtx, sizeof(*p));
  if( p ){
    if( p->nTotal>1 ){
      double r = (double)(p->nValue-1) / (double)(p->nTotal-1);
      sqlite3_result_double(pCtx, r);

  if( p ){
    if( p->nTotal==0 ){
      p->nTotal = sqlite3_value_int64(apArg[0]);
    }
    p->nStep++;
  }
}






static void cume_distValueFunc(sqlite3_context *pCtx){
  struct CallCount *p;
  p = (struct CallCount*)sqlite3_aggregate_context(pCtx, sizeof(*p));
  if( p && p->nTotal ){
    double r = (double)(p->nStep) / (double)(p->nTotal);
    sqlite3_result_double(pCtx, r);
  }

            pCtx, "argument of ntile must be a positive integer", -1
        );
      }
    }
    p->iRow++;
  }
}






static void ntileValueFunc(sqlite3_context *pCtx){
  struct NtileCtx *p;
  p = (struct NtileCtx*)sqlite3_aggregate_context(pCtx, sizeof(*p));
  if( p && p->nParam>0 ){
    int nSize = (p->nTotal / p->nParam);
    if( nSize==0 ){
      sqlite3_result_int64(pCtx, p->iRow);

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

/*
** Static names for the built-in window function names.  These static
** names are used, rather than string literals, so that FuncDef objects
** can be associated with a particular window function by direct
** comparison of the zName pointer.  Example:
**
**       if( pFuncDef->zName==row_valueName ){ ... }
*/
static const char row_numberName[] =   "row_number";
static const char dense_rankName[] =   "dense_rank";
static const char rankName[] =         "rank";
static const char percent_rankName[] = "percent_rank";
static const char cume_distName[] =    "cume_dist";
static const char ntileName[] =        "ntile";
static const char last_valueName[] =   "last_value";
static const char nth_valueName[] =    "nth_value";
static const char first_valueName[] =  "first_value";
static const char leadName[] =         "lead";
static const char lagName[] =          "lag";

/*
** No-op implementations of xStep() and xFinalize().  Used as place-holders
** for built-in window functions that never call those interfaces.
**
** The noopValueFunc() is called but is expected to do nothing.  The
** noopStepFunc() is never called, and so it is marked with NO_TEST to
** let the test coverage routine know not to expect this function to be
** invoked.
*/
static void noopStepFunc(    /*NO_TEST*/
  sqlite3_context *p,        /*NO_TEST*/
  int n,                     /*NO_TEST*/
  sqlite3_value **a          /*NO_TEST*/
){                           /*NO_TEST*/
  assert(0);                 /*NO_TEST*/

}                            /*NO_TEST*/
static void noopValueFunc(sqlite3_context *p){ /*no-op*/; }

/* Window functions that use all window interfaces: xStep, xFinal,
** xValue, and xInverse */
#define WINDOWFUNCALL(name,nArg,extra) {                                   \
  nArg, (SQLITE_UTF8|SQLITE_FUNC_WINDOW|extra), 0, 0,                      \
  name ## StepFunc, name ## FinalizeFunc, name ## ValueFunc,               \
  name ## InvFunc, name ## Name                                            \
}

/* Window functions that are implemented using bytecode and thus have
** no-op routines for their methods */
#define WINDOWFUNCNOOP(name,nArg,extra) {                                  \
  nArg, (SQLITE_UTF8|SQLITE_FUNC_WINDOW|extra), 0, 0,                      \
  noopStepFunc, noopValueFunc, noopValueFunc,                              \
  noopStepFunc, name ## Name                                               \
}

/* Window functions that use all window interfaces: xStep, the
** same routine for xFinalize and xValue and which never call
** xInverse. */
#define WINDOWFUNCX(name,nArg,extra) {                                     \
  nArg, (SQLITE_UTF8|SQLITE_FUNC_WINDOW|extra), 0, 0,                      \
  name ## StepFunc, name ## ValueFunc, name ## ValueFunc,                  \
  noopStepFunc, name ## Name                                               \
}


/*
** Register those built-in window functions that are not also aggregates.
*/
void sqlite3WindowFunctions(void){
  static FuncDef aWindowFuncs[] = {
    WINDOWFUNCX(row_number, 0, 0),
    WINDOWFUNCX(dense_rank, 0, 0),
    WINDOWFUNCX(rank, 0, 0),
    WINDOWFUNCX(percent_rank, 0, SQLITE_FUNC_WINDOW_SIZE),
    WINDOWFUNCX(cume_dist, 0, SQLITE_FUNC_WINDOW_SIZE),
    WINDOWFUNCX(ntile, 1, SQLITE_FUNC_WINDOW_SIZE),
    WINDOWFUNCALL(last_value, 1, 0),
    WINDOWFUNCNOOP(nth_value, 2, 0),
    WINDOWFUNCNOOP(first_value, 1, 0),
    WINDOWFUNCNOOP(lead, 1, 0),
    WINDOWFUNCNOOP(lead, 2, 0),
    WINDOWFUNCNOOP(lead, 3, 0),
    WINDOWFUNCNOOP(lag, 1, 0),
    WINDOWFUNCNOOP(lag, 2, 0),
    WINDOWFUNCNOOP(lag, 3, 0),
  };
  sqlite3InsertBuiltinFuncs(aWindowFuncs, ArraySize(aWindowFuncs));
}

/*
** This function is called immediately after resolving the function name
** for a window function within a SELECT statement. Argument pList is a

  if( pFunc->funcFlags & SQLITE_FUNC_WINDOW ){
    sqlite3 *db = pParse->db;
    if( pWin->pFilter ){
      sqlite3ErrorMsg(pParse, 
          "FILTER clause may only be used with aggregate window functions"
      );
    }else
    if( pFunc->zName==row_numberName || pFunc->zName==ntileName ){
      sqlite3ExprDelete(db, pWin->pStart);
      sqlite3ExprDelete(db, pWin->pEnd);
      pWin->pStart = pWin->pEnd = 0;
      pWin->eType = TK_ROWS;
      pWin->eStart = TK_UNBOUNDED;
      pWin->eEnd = TK_CURRENT;
    }else

    if( pFunc->zName==dense_rankName || pFunc->zName==rankName
     || pFunc->zName==percent_rankName || pFunc->zName==cume_distName
    ){
      sqlite3ExprDelete(db, pWin->pStart);
      sqlite3ExprDelete(db, pWin->pEnd);
      pWin->pStart = pWin->pEnd = 0;
      pWin->eType = TK_RANGE;
      pWin->eStart = TK_UNBOUNDED;
      pWin->eEnd = TK_CURRENT;

        assert( pKeyInfo->aSortOrder[0]==0 );
        pKeyInfo->aSortOrder[0] = 1;
      }
      sqlite3VdbeAddOp2(v, OP_OpenEphemeral, pWin->csrApp, 2);
      sqlite3VdbeAppendP4(v, pKeyInfo, P4_KEYINFO);
      sqlite3VdbeAddOp2(v, OP_Integer, 0, pWin->regApp+1);
    }
    else if( p->zName==nth_valueName || p->zName==first_valueName ){
      /* Allocate two registers at pWin->regApp. These will be used to
      ** store the start and end index of the current frame.  */
      assert( pMWin->iEphCsr );
      pWin->regApp = pParse->nMem+1;
      pWin->csrApp = pParse->nTab++;
      pParse->nMem += 2;
      sqlite3VdbeAddOp2(v, OP_OpenDup, pWin->csrApp, pMWin->iEphCsr);
    }
    else if( p->zName==leadName || p->zName==lagName ){
      assert( pMWin->iEphCsr );
      pWin->csrApp = pParse->nTab++;
      sqlite3VdbeAddOp2(v, OP_OpenDup, pWin->csrApp, pMWin->iEphCsr);
    }
  }
}

        sqlite3VdbeAddOp4Int(v, OP_SeekGE, pWin->csrApp, 0, regArg, 1);
        VdbeCoverage(v);
        sqlite3VdbeAddOp1(v, OP_Delete, pWin->csrApp);
        sqlite3VdbeJumpHere(v, sqlite3VdbeCurrentAddr(v)-2);
      }
      sqlite3VdbeJumpHere(v, addrIsNull);
    }else if( pWin->regApp ){
      assert( pWin->pFunc->zName==nth_valueName
           || pWin->pFunc->zName==first_valueName
      );
      assert( bInverse==0 || bInverse==1 );
      sqlite3VdbeAddOp2(v, OP_AddImm, pWin->regApp+1-bInverse, 1);
    }else if( pWin->pFunc->zName==leadName
           || pWin->pFunc->zName==lagName
    ){
      /* no-op */
    }else{
      int addrIf = 0;
      if( pWin->pFilter ){
        int regTmp;
        assert( nArg==pWin->pOwner->x.pList->nExpr );

  int regGosub,
  int addrGosub
){
  Vdbe *v = sqlite3GetVdbe(pParse);
  Window *pWin;
  for(pWin=pMWin; pWin; pWin=pWin->pNextWin){
    FuncDef *pFunc = pWin->pFunc;
    if( pFunc->zName==nth_valueName
     || pFunc->zName==first_valueName
    ){
      int csr = pWin->csrApp;
      int lbl = sqlite3VdbeMakeLabel(v);
      int tmpReg = sqlite3GetTempReg(pParse);
      sqlite3VdbeAddOp2(v, OP_Null, 0, pWin->regResult);

      if( pFunc->zName==nth_valueName ){
        sqlite3VdbeAddOp3(v, OP_Column, pMWin->iEphCsr, pWin->iArgCol+1,tmpReg);
      }else{
        sqlite3VdbeAddOp2(v, OP_Integer, 1, tmpReg);
      }
      sqlite3VdbeAddOp3(v, OP_Add, tmpReg, pWin->regApp, tmpReg);
      sqlite3VdbeAddOp3(v, OP_Gt, pWin->regApp+1, lbl, tmpReg);
      VdbeCoverage(v);
      sqlite3VdbeAddOp3(v, OP_SeekRowid, csr, lbl, tmpReg);
      VdbeCoverage(v);
      sqlite3VdbeAddOp3(v, OP_Column, csr, pWin->iArgCol, pWin->regResult);
      sqlite3VdbeResolveLabel(v, lbl);
      sqlite3ReleaseTempReg(pParse, tmpReg);
    }
    else if( pFunc->zName==leadName || pFunc->zName==lagName ){
      int nArg = pWin->pOwner->x.pList->nExpr;
      int iEph = pMWin->iEphCsr;
      int csr = pWin->csrApp;
      int lbl = sqlite3VdbeMakeLabel(v);
      int tmpReg = sqlite3GetTempReg(pParse);

      if( 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( nArg<2 ){
        int val = (pFunc->zName==leadName ? 1 : -1);
        sqlite3VdbeAddOp2(v, OP_AddImm, tmpReg, val);
      }else{
        int op = (pFunc->zName==leadName ? OP_Add : OP_Subtract);
        int tmpReg2 = sqlite3GetTempReg(pParse);
        sqlite3VdbeAddOp3(v, OP_Column, iEph, pWin->iArgCol+1, tmpReg2);
        sqlite3VdbeAddOp3(v, op, tmpReg2, tmpReg, tmpReg);
        sqlite3ReleaseTempReg(pParse, tmpReg2);
      }

      sqlite3VdbeAddOp3(v, OP_SeekRowid, csr, lbl, tmpReg);

  int regArg;
  int nArg = 0;
  Window *pWin;
  for(pWin=pMWin; pWin; pWin=pWin->pNextWin){
    FuncDef *pFunc = pWin->pFunc;
    sqlite3VdbeAddOp2(v, OP_Null, 0, pWin->regAccum);
    nArg = MAX(nArg, windowArgCount(pWin));
    if( pFunc->zName==nth_valueName
     || pFunc->zName==first_valueName
    ){
      sqlite3VdbeAddOp2(v, OP_Integer, 0, pWin->regApp);
      sqlite3VdbeAddOp2(v, OP_Integer, 0, pWin->regApp+1);
    }

    if( (pFunc->funcFlags & SQLITE_FUNC_MINMAX) && pWin->csrApp ){
      assert( pWin->eStart!=TK_UNBOUNDED );

    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->zName==nth_valueName)
         || (pFunc->zName==first_valueName)
         || (pFunc->zName==leadName)
         || (pFunc->zName==lagName)
        ){
          bCache = 1;
          break;
        }
      }
    }