assert( pCur->pgnoRoot==0 || pCur->pPage->nCell==0 );
    *pRes = 1;
    rc = SQLITE_OK;
  }
  return rc;
}






void sqlite3BtreeSkipNext(BtCursor *pCur){
  if( pCur->eState==CURSOR_VALID ){
    pCur->eState = CURSOR_SKIPNEXT;
    pCur->skipNext = 1;
  }
}

    assert( pCur->pgnoRoot==0 || pCur->pPage->nCell==0 );
    *pRes = 1;
    rc = SQLITE_OK;
  }
  return rc;
}

/*
** This function is a no-op if cursor pCur does not point to a valid row.
** Otherwise, if pCur is valid, configure it so that the next call to
** sqlite3BtreeNext() is a no-op.
*/
void sqlite3BtreeSkipNext(BtCursor *pCur){
  if( pCur->eState==CURSOR_VALID ){
    pCur->eState = CURSOR_SKIPNEXT;
    pCur->skipNext = 1;
  }
}

**   window frame is sometimes modified before the SELECT statement is
**   rewritten. For example, regardless of the specified window frame, the
**   row_number() function always uses:
**
**     ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
**
**   See sqlite3WindowUpdate() for details.





*/

/*
** Implementation of built-in window function row_number(). Assumes that the
** window frame has been coerced to:
**
**   ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
................................................................................
    WINDOWFUNC(first_value, 1, 0),
    WINDOWFUNC(lead, 1, 0), WINDOWFUNC(lead, 2, 0), WINDOWFUNC(lead, 3, 0),
    WINDOWFUNC(lag, 1, 0),  WINDOWFUNC(lag, 2, 0),  WINDOWFUNC(lag, 3, 0),
  };
  sqlite3InsertBuiltinFuncs(aWindowFuncs, ArraySize(aWindowFuncs));
}


















void sqlite3WindowUpdate(
  Parse *pParse, 
  Window *pList, 

  Window *pWin, 
  FuncDef *pFunc

){
  if( pWin->zName ){
    Window *p;
    for(p=pList; p; p=p->pNextWin){
      if( sqlite3StrICmp(p->zName, pWin->zName)==0 ) break;
    }
    if( p==0 ){
................................................................................
      pWin->eStart = TK_UNBOUNDED;
      pWin->eEnd = TK_CURRENT;
    }
  }
  pWin->pFunc = pFunc;
}





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

static int selectWindowRewriteSelectCb(Walker *pWalker, Select *pSelect){
  return WRC_Prune;
}


static int selectWindowRewriteExprCb(Walker *pWalker, Expr *pExpr){
  struct WindowRewrite *p = pWalker->u.pRewrite;
  Parse *pParse = pWalker->pParse;

  switch( pExpr->op ){

    case TK_FUNCTION:
................................................................................

    default: /* no-op */
      break;
  }

  return WRC_Continue;
}


















static int selectWindowRewriteEList(
  Parse *pParse, 
  Window *pWin,
  ExprList *pEList,               /* Rewrite expressions in this list */
  ExprList **ppSub                /* IN/OUT: Sub-select expression-list */
){
  Walker sWalker;
................................................................................

  rc = sqlite3WalkExprList(&sWalker, pEList);

  *ppSub = sRewrite.pSub;
  return rc;
}





static ExprList *exprListAppendList(
  Parse *pParse,          /* Parsing context */
  ExprList *pList,        /* List to which to append. Might be NULL */
  ExprList *pAppend       /* List of values to append. Might be NULL */
){
  if( pAppend ){
    int i;
................................................................................
  return pList;
}

/*
** If the SELECT statement passed as the second argument does not invoke
** any SQL window functions, this function is a no-op. Otherwise, it 
** rewrites the SELECT statement so that window function xStep functions
** are invoked in the correct order. The simplest version of the 
** transformation is:
**
**   SELECT win(args...) OVER (<list1>) FROM <src> ORDER BY <list2>
**
** to
**
**   SELECT win(args...) FROM (
**     SELECT args... FROM <src> ORDER BY <list1>
**   ) ORDER BY <list2>
**
** where <src> may contain WHERE, GROUP BY and HAVING clauses, and <list1>
** is the concatenation of the PARTITION BY and ORDER BY clauses in the
** OVER clause.
**
*/
int sqlite3WindowRewrite(Parse *pParse, Select *p){
  int rc = SQLITE_OK;
  if( p->pWin ){
    Vdbe *v = sqlite3GetVdbe(pParse);
    int i;
    sqlite3 *db = pParse->db;
................................................................................

    sqlite3VdbeAddOp2(v, OP_OpenEphemeral, pMWin->iEphCsr, pSublist->nExpr);
  }

  return rc;
}




void sqlite3WindowDelete(sqlite3 *db, Window *p){
  if( p ){
    sqlite3ExprDelete(db, p->pFilter);
    sqlite3ExprListDelete(db, p->pPartition);
    sqlite3ExprListDelete(db, p->pOrderBy);
    sqlite3ExprDelete(db, p->pEnd);
    sqlite3ExprDelete(db, p->pStart);
    sqlite3DbFree(db, p->zName);
    sqlite3DbFree(db, p);
  }
}




void sqlite3WindowListDelete(sqlite3 *db, Window *p){
  while( p ){
    Window *pNext = p->pNextWin;
    sqlite3WindowDelete(db, p);
    p = pNext;
  }
}




Window *sqlite3WindowAlloc(
  Parse *pParse, 
  int eType,
  int eStart, Expr *pStart,
  int eEnd, Expr *pEnd
){
  Window *pWin = (Window*)sqlite3DbMallocZero(pParse->db, sizeof(Window));
................................................................................
    sqlite3ExprDelete(pParse->db, pEnd);
    sqlite3ExprDelete(pParse->db, pStart);
  }

  return pWin;
}




void sqlite3WindowAttach(Parse *pParse, Expr *p, Window *pWin){
  if( p ){
    p->pWin = pWin;
    if( pWin ) pWin->pOwner = p;
  }else{
    sqlite3WindowDelete(pParse->db, pWin);
  }

**   window frame is sometimes modified before the SELECT statement is
**   rewritten. For example, regardless of the specified window frame, the
**   row_number() function always uses:
**
**     ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
**
**   See sqlite3WindowUpdate() for details.
**
**   As well as some of the built-in window functions, aggregate window
**   functions min() and max() are implemented using VDBE instructions if
**   the start of the window frame is declared as anything other than 
**   UNBOUNDED PRECEDING.
*/

/*
** Implementation of built-in window function row_number(). Assumes that the
** window frame has been coerced to:
**
**   ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
................................................................................
    WINDOWFUNC(first_value, 1, 0),
    WINDOWFUNC(lead, 1, 0), WINDOWFUNC(lead, 2, 0), WINDOWFUNC(lead, 3, 0),
    WINDOWFUNC(lag, 1, 0),  WINDOWFUNC(lag, 2, 0),  WINDOWFUNC(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
** linked list of WINDOW definitions for the current SELECT statement.
** Argument pFunc is the function definition just resolved and pWin
** is the Window object representing the associated OVER clause. This
** function updates the contents of pWin as follows:
**
**   * If the OVER clause refered to a named window (as in "max(x) OVER win"),
**     search list pList for a matching WINDOW definition, and update pWin
**     accordingly. If no such WINDOW clause can be found, leave an error
**     in pParse.
**
**   * If the function is a built-in window function that requires the
**     window to be coerced (see "BUILT-IN WINDOW FUNCTIONS" at the top
**     of this file), pWin is updated here.
*/
void sqlite3WindowUpdate(
  Parse *pParse, 

  Window *pList,                  /* List of named windows for this SELECT */
  Window *pWin,                   /* Window frame to update */

  FuncDef *pFunc                  /* Window function definition */
){
  if( pWin->zName ){
    Window *p;
    for(p=pList; p; p=p->pNextWin){
      if( sqlite3StrICmp(p->zName, pWin->zName)==0 ) break;
    }
    if( p==0 ){
................................................................................
      pWin->eStart = TK_UNBOUNDED;
      pWin->eEnd = TK_CURRENT;
    }
  }
  pWin->pFunc = pFunc;
}

/*
** Context object passed through sqlite3WalkExprList() to
** selectWindowRewriteExprCb() by selectWindowRewriteEList().
*/
typedef struct WindowRewrite WindowRewrite;
struct WindowRewrite {
  Window *pWin;
  ExprList *pSub;
};

/*
** Callback function used by selectWindowRewriteEList(). If necessary,
** this function appends to the output expression-list and updates 
** expression (*ppExpr) in place.
*/
static int selectWindowRewriteExprCb(Walker *pWalker, Expr *pExpr){
  struct WindowRewrite *p = pWalker->u.pRewrite;
  Parse *pParse = pWalker->pParse;

  switch( pExpr->op ){

    case TK_FUNCTION:
................................................................................

    default: /* no-op */
      break;
  }

  return WRC_Continue;
}
static int selectWindowRewriteSelectCb(Walker *pWalker, Select *pSelect){
  return WRC_Prune;
}


/*
** Iterate through each expression in expression-list pEList. For each:
**
**   * TK_COLUMN,
**   * aggregate function, or
**   * window function with a Window object that is not a member of the 
**     linked list passed as the second argument (pWin)
**
** Append the node to output expression-list (*ppSub). And replace it
** with a TK_COLUMN that reads the (N-1)th element of table 
** pWin->iEphCsr, where N is the number of elements in (*ppSub) after
** appending the new one.
*/
static int selectWindowRewriteEList(
  Parse *pParse, 
  Window *pWin,
  ExprList *pEList,               /* Rewrite expressions in this list */
  ExprList **ppSub                /* IN/OUT: Sub-select expression-list */
){
  Walker sWalker;
................................................................................

  rc = sqlite3WalkExprList(&sWalker, pEList);

  *ppSub = sRewrite.pSub;
  return rc;
}

/*
** Append a copy of each expression in expression-list pAppend to
** expression list pList. Return a pointer to the result list.
*/
static ExprList *exprListAppendList(
  Parse *pParse,          /* Parsing context */
  ExprList *pList,        /* List to which to append. Might be NULL */
  ExprList *pAppend       /* List of values to append. Might be NULL */
){
  if( pAppend ){
    int i;
................................................................................
  return pList;
}

/*
** If the SELECT statement passed as the second argument does not invoke
** any SQL window functions, this function is a no-op. Otherwise, it 
** rewrites the SELECT statement so that window function xStep functions
** are invoked in the correct order as described under "SELECT REWRITING"
** at the top of this file.













*/
int sqlite3WindowRewrite(Parse *pParse, Select *p){
  int rc = SQLITE_OK;
  if( p->pWin ){
    Vdbe *v = sqlite3GetVdbe(pParse);
    int i;
    sqlite3 *db = pParse->db;
................................................................................

    sqlite3VdbeAddOp2(v, OP_OpenEphemeral, pMWin->iEphCsr, pSublist->nExpr);
  }

  return rc;
}

/*
** Free the Window object passed as the second argument.
*/
void sqlite3WindowDelete(sqlite3 *db, Window *p){
  if( p ){
    sqlite3ExprDelete(db, p->pFilter);
    sqlite3ExprListDelete(db, p->pPartition);
    sqlite3ExprListDelete(db, p->pOrderBy);
    sqlite3ExprDelete(db, p->pEnd);
    sqlite3ExprDelete(db, p->pStart);
    sqlite3DbFree(db, p->zName);
    sqlite3DbFree(db, p);
  }
}

/*
** Free the linked list of Window objects starting at the second argument.
*/
void sqlite3WindowListDelete(sqlite3 *db, Window *p){
  while( p ){
    Window *pNext = p->pNextWin;
    sqlite3WindowDelete(db, p);
    p = pNext;
  }
}

/*
** Allocate and return a new Window object.
*/
Window *sqlite3WindowAlloc(
  Parse *pParse, 
  int eType,
  int eStart, Expr *pStart,
  int eEnd, Expr *pEnd
){
  Window *pWin = (Window*)sqlite3DbMallocZero(pParse->db, sizeof(Window));
................................................................................
    sqlite3ExprDelete(pParse->db, pEnd);
    sqlite3ExprDelete(pParse->db, pStart);
  }

  return pWin;
}

/*
** Attach window object pWin to expression p.
*/
void sqlite3WindowAttach(Parse *pParse, Expr *p, Window *pWin){
  if( p ){
    p->pWin = pWin;
    if( pWin ) pWin->pOwner = p;
  }else{
    sqlite3WindowDelete(pParse->db, pWin);
  }

  INSERT INTO ttt VALUES(8, 2, 4);
  INSERT INTO ttt VALUES(9, 3, 5);
}

execsql_test 4.1 {
  SELECT max(c), max(b) OVER (ORDER BY b) FROM ttt GROUP BY b;
}










finish_test

  INSERT INTO ttt VALUES(8, 2, 4);
  INSERT INTO ttt VALUES(9, 3, 5);
}

execsql_test 4.1 {
  SELECT max(c), max(b) OVER (ORDER BY b) FROM ttt GROUP BY b;
}

execsql_test 4.2 {
  SELECT max(b) OVER (ORDER BY max(c)) FROM ttt GROUP BY b;
}

execsql_test 4.3 {
  SELECT abs(max(b) OVER (ORDER BY b)) FROM ttt GROUP BY b;
}


finish_test

  INSERT INTO ttt VALUES(8, 2, 4);
  INSERT INTO ttt VALUES(9, 3, 5);
} {}

do_execsql_test 4.1 {
  SELECT max(c), max(b) OVER (ORDER BY b) FROM ttt GROUP BY b;
} {3 1   4 2   5 3}









finish_test

  INSERT INTO ttt VALUES(8, 2, 4);
  INSERT INTO ttt VALUES(9, 3, 5);
} {}

do_execsql_test 4.1 {
  SELECT max(c), max(b) OVER (ORDER BY b) FROM ttt GROUP BY b;
} {3 1   4 2   5 3}

do_execsql_test 4.2 {
  SELECT max(b) OVER (ORDER BY max(c)) FROM ttt GROUP BY b;
} {1   2   3}

do_execsql_test 4.3 {
  SELECT abs(max(b) OVER (ORDER BY b)) FROM ttt GROUP BY b;
} {1   2   3}

finish_test