4 files changed, 63 insertions, 11 deletions

diff --git a/src/func.c b/src/func.c
index c5dd6a58e..ff7c3049f 100644
--- a/src/func.c
+++ b/src/func.c
@@ -1572,6 +1572,9 @@ static void totalFinalize(sqlite3_context *context){
 typedef struct CountCtx CountCtx;
 struct CountCtx {
   i64 n;
+#ifdef SQLITE_DEBUG
+  int bInverse;                   /* True if xInverse() ever called */
+#endif
 };
 
 /*
@@ -1589,7 +1592,7 @@ static void countStep(sqlite3_context *context, int argc, sqlite3_value **argv){
   ** sure it still operates correctly, verify that its count agrees with our 
   ** internal count when using count(*) and when the total count can be
   ** expressed as a 32-bit integer. */
-  assert( argc==1 || p==0 || p->n>0x7fffffff
+  assert( argc==1 || p==0 || p->n>0x7fffffff || p->bInverse
           || p->n==sqlite3_aggregate_count(context) );
 #endif
 }   
@@ -1598,6 +1601,18 @@ static void countFinalize(sqlite3_context *context){
   p = sqlite3_aggregate_context(context, 0);
   sqlite3_result_int64(context, p ? p->n : 0);
 }
+#ifndef SQLITE_OMIT_WINDOWFUNC
+static void countInverse(sqlite3_context *ctx, int argc, sqlite3_value **argv){
+  CountCtx *p;
+  p = sqlite3_aggregate_context(ctx, sizeof(*p));
+  if( (argc==0 || SQLITE_NULL!=sqlite3_value_type(argv[0])) && p ){
+    p->n--;
+#ifdef SQLITE_DEBUG
+    p->bInverse = 1;
+#endif
+  }
+}   
+#endif
 
 /*
 ** Routines to implement min() and max() aggregate functions.
@@ -1943,8 +1958,10 @@ void sqlite3RegisterBuiltinFunctions(void){
     WAGGREGATE(sum,   1,0,0, sumStep, sumFinalize, sumFinalize, sumInverse, 0),
     WAGGREGATE(total, 1,0,0, sumStep,totalFinalize,totalFinalize,sumInverse, 0),
     WAGGREGATE(avg,   1,0,0, sumStep, avgFinalize, avgFinalize, sumInverse, 0),
-    AGGREGATE2(count, 0,0,0, countStep, countFinalize, SQLITE_FUNC_COUNT  ),
-    WAGGREGATE(count, 1,0,0, countStep, countFinalize, 0, 0, 0 ),
+    WAGGREGATE(count, 0,0,0, countStep, 
+        countFinalize, countFinalize, countInverse, SQLITE_FUNC_COUNT  ),
+    WAGGREGATE(count, 1,0,0, countStep, 
+        countFinalize, countFinalize, countInverse, 0  ),
     WAGGREGATE(group_concat, 1, 0, 0, groupConcatStep, 
         groupConcatFinalize, groupConcatValue, groupConcatInverse, 0),
     WAGGREGATE(group_concat, 2, 0, 0, groupConcatStep, 
diff --git a/src/resolve.c b/src/resolve.c
index b6389eba6..7c1d4b162 100644
--- a/src/resolve.c
+++ b/src/resolve.c
@@ -758,7 +758,11 @@ static int resolveExprStep(Walker *pWalker, Expr *pExpr){
       }
 
 #ifndef SQLITE_OMIT_WINDOWFUNC
-      if( is_agg==0 && pExpr->pWin ){
+      assert( is_agg==0 || (pDef->funcFlags & SQLITE_FUNC_MINMAX)
+          || (pDef->xValue==0 && pDef->xInverse==0)
+          || (pDef->xValue && pDef->xInverse && pDef->xSFunc && pDef->xFinalize)
+      );
+      if( pDef && pDef->xValue==0 && pExpr->pWin ){
         sqlite3ErrorMsg(pParse, 
             "%.*s() may not be used as a window function", nId, zId
         );
diff --git a/src/test_window.c b/src/test_window.c
index 576c58f6c..1b43c2717 100644
--- a/src/test_window.c
+++ b/src/test_window.c
@@ -302,6 +302,32 @@ static int SQLITE_TCLAPI test_create_sumint(
   return TCL_OK;
 }
 
+static int SQLITE_TCLAPI test_override_sum(
+  void * clientData,
+  Tcl_Interp *interp,
+  int objc,
+  Tcl_Obj *CONST objv[]
+){
+  sqlite3 *db;
+  int rc;
+
+  if( objc!=2 ){
+    Tcl_WrongNumArgs(interp, 1, objv, "DB");
+    return TCL_ERROR;
+  }
+  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
+
+  rc = sqlite3_create_function(db, "sum", -1, SQLITE_UTF8, 0,
+      0, sumintStep, sumintFinal
+  );
+
+  if( rc!=SQLITE_OK ){
+    Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
+    return TCL_ERROR;
+  }
+  return TCL_OK;
+}
+
 int Sqlitetest_window_Init(Tcl_Interp *interp){
   static struct {
      char *zName;
@@ -311,6 +337,7 @@ int Sqlitetest_window_Init(Tcl_Interp *interp){
      { "sqlite3_create_window_function", test_create_window, 0 },
      { "test_create_window_function_misuse", test_create_window_misuse, 0 },
      { "test_create_sumint", test_create_sumint, 0 },
+     { "test_override_sum", test_override_sum, 0 },
   };
   int i;
   for(i=0; i<sizeof(aObjCmd)/sizeof(aObjCmd[0]); i++){
diff --git a/src/window.c b/src/window.c
index 744771933..6cc9b7edd 100644
--- a/src/window.c
+++ b/src/window.c
@@ -1594,17 +1594,21 @@ static void windowCodeRowExprStep(
    || pMWin->eStart==TK_PRECEDING 
    || pMWin->eStart==TK_FOLLOWING 
   ){
-    int addrJumpHere = 0;
+    int lblSkipInverse = sqlite3VdbeMakeLabel(v);;
     if( pMWin->eStart==TK_PRECEDING ){
-      addrJumpHere = sqlite3VdbeAddOp3(v, OP_IfPos, regStart, 0 , 1);
+      sqlite3VdbeAddOp3(v, OP_IfPos, regStart, lblSkipInverse, 1);
       VdbeCoverage(v);
     }
-    sqlite3VdbeAddOp2(v, OP_Next, csrStart, sqlite3VdbeCurrentAddr(v)+1);
-    VdbeCoverage(v);
-    windowAggStep(pParse, pMWin, csrStart, 1, regArg, regSize);
-    if( addrJumpHere ){
-      sqlite3VdbeJumpHere(v, addrJumpHere);
+    if( pMWin->eStart==TK_FOLLOWING ){
+      sqlite3VdbeAddOp2(v, OP_Next, csrStart, sqlite3VdbeCurrentAddr(v)+2);
+      VdbeCoverage(v);
+      sqlite3VdbeAddOp2(v, OP_Goto, 0, lblSkipInverse);
+    }else{
+      sqlite3VdbeAddOp2(v, OP_Next, csrStart, sqlite3VdbeCurrentAddr(v)+1);
+      VdbeCoverage(v);
     }
+    windowAggStep(pParse, pMWin, csrStart, 1, regArg, regSize);
+    sqlite3VdbeResolveLabel(v, lblSkipInverse);
   }
   if( pMWin->eEnd==TK_FOLLOWING ){
     sqlite3VdbeJumpHere(v, addrIfPos1);