Add support for attaching a FILTER clause to an aggregate function.

FossilOrigin-Name: ee293e5aeac0b05a8b809095610fd8b4fdaf8e68cd368de90ec0d45e3582ffe5

10 files changed, 146 insertions, 82 deletions

diff --git a/src/btree.c b/src/btree.c
index 6c73a9422..5f82f1cc0 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -8307,11 +8307,13 @@ static int balance(BtCursor *pCur){
   VVA_ONLY( int balance_deeper_called = 0 );
 
   do {
-    int iPage = pCur->iPage;
+    int iPage;
     MemPage *pPage = pCur->pPage;
 
     if( NEVER(pPage->nFree<0) && btreeComputeFreeSpace(pPage) ) break;
-    if( iPage==0 ){
+    if( pPage->nOverflow==0 && pPage->nFree<=nMin ){
+      break;
+    }else if( (iPage = pCur->iPage)==0 ){
       if( pPage->nOverflow ){
         /* The root page of the b-tree is overfull. In this case call the
         ** balance_deeper() function to create a new child for the root-page
@@ -8332,8 +8334,6 @@ static int balance(BtCursor *pCur){
       }else{
         break;
       }
-    }else if( pPage->nOverflow==0 && pPage->nFree<=nMin ){
-      break;
     }else{
       MemPage * const pParent = pCur->apPage[iPage-1];
       int const iIdx = pCur->aiIdx[iPage-1];
diff --git a/src/expr.c b/src/expr.c
index c4f201a13..9ba81a845 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -1040,15 +1040,18 @@ static SQLITE_NOINLINE void sqlite3ExprDeleteNN(sqlite3 *db, Expr *p){
     assert( p->x.pList==0 || p->pRight==0 );
     if( p->pLeft && p->op!=TK_SELECT_COLUMN ) sqlite3ExprDeleteNN(db, p->pLeft);
     if( p->pRight ){
+      assert( !ExprHasProperty(p, EP_WinFunc) );
       sqlite3ExprDeleteNN(db, p->pRight);
     }else if( ExprHasProperty(p, EP_xIsSelect) ){
+      assert( !ExprHasProperty(p, EP_WinFunc) );
       sqlite3SelectDelete(db, p->x.pSelect);
     }else{
       sqlite3ExprListDelete(db, p->x.pList);
-    }
-    if( ExprHasProperty(p, EP_WinFunc) ){
-      assert( p->op==TK_FUNCTION );
-      sqlite3WindowDelete(db, p->y.pWin);
+#ifndef SQLITE_OMIT_WINDOWFUNC
+      if( ExprHasProperty(p, EP_WinFunc) ){
+        sqlite3WindowDelete(db, p->y.pWin);
+      }
+#endif
     }
   }
   if( ExprHasProperty(p, EP_MemToken) ) sqlite3DbFree(db, p->u.zToken);
@@ -1332,8 +1335,9 @@ static With *withDup(sqlite3 *db, With *p){
 ** objects found there, assembling them onto the linked list at Select->pWin.
 */
 static int gatherSelectWindowsCallback(Walker *pWalker, Expr *pExpr){
-  if( pExpr->op==TK_FUNCTION && pExpr->y.pWin!=0 ){
-    assert( ExprHasProperty(pExpr, EP_WinFunc) );
+  if( pExpr->op==TK_FUNCTION && ExprHasProperty(pExpr, EP_WinFunc) ){
+    assert( pExpr->y.pWin );
+    assert( IsWindowFunc(pExpr) );
     pExpr->y.pWin->pNextWin = pWalker->u.pSelect->pWin;
     pWalker->u.pSelect->pWin = pExpr->y.pWin;
   }
@@ -4839,20 +4843,17 @@ int sqlite3ExprCompare(Parse *pParse, Expr *pA, Expr *pB, int iTab){
     return 2;
   }
   if( pA->op!=TK_COLUMN && pA->op!=TK_AGG_COLUMN && pA->u.zToken ){
-    if( pA->op==TK_FUNCTION ){
+    if( pA->op==TK_FUNCTION || pA->op==TK_AGG_FUNCTION ){
       if( sqlite3StrICmp(pA->u.zToken,pB->u.zToken)!=0 ) return 2;
 #ifndef SQLITE_OMIT_WINDOWFUNC
-      /* Justification for the assert():
-      ** window functions have p->op==TK_FUNCTION but aggregate functions
-      ** have p->op==TK_AGG_FUNCTION.  So any comparison between an aggregate
-      ** function and a window function should have failed before reaching
-      ** this point.  And, it is not possible to have a window function and
-      ** a scalar function with the same name and number of arguments.  So
-      ** if we reach this point, either A and B both window functions or
-      ** neither are a window functions. */
-      assert( ExprHasProperty(pA,EP_WinFunc)==ExprHasProperty(pB,EP_WinFunc) );
+      assert( pA->op==pB->op );
+      if( ExprHasProperty(pA,EP_WinFunc)!=ExprHasProperty(pB,EP_WinFunc) ){
+        return 2;
+      }
       if( ExprHasProperty(pA,EP_WinFunc) ){
-        if( sqlite3WindowCompare(pParse,pA->y.pWin,pB->y.pWin)!=0 ) return 2;
+        if( sqlite3WindowCompare(pParse, pA->y.pWin, pB->y.pWin, 1)!=0 ){
+          return 2;
+        }
       }
 #endif
     }else if( pA->op==TK_NULL ){
diff --git a/src/parse.y b/src/parse.y
index fc5bff16d..7a3835a62 100644
--- a/src/parse.y
+++ b/src/parse.y
@@ -1044,11 +1044,11 @@ expr(A) ::= id(X) LP STAR RP. {
 }
 
 %ifndef SQLITE_OMIT_WINDOWFUNC
-expr(A) ::= id(X) LP distinct(D) exprlist(Y) RP over_clause(Z). {
+expr(A) ::= id(X) LP distinct(D) exprlist(Y) RP filter_over(Z). {
   A = sqlite3ExprFunction(pParse, Y, &X, D);
   sqlite3WindowAttach(pParse, A, Z);
 }
-expr(A) ::= id(X) LP STAR RP over_clause(Z). {
+expr(A) ::= id(X) LP STAR RP filter_over(Z). {
   A = sqlite3ExprFunction(pParse, 0, &X, 0);
   sqlite3WindowAttach(pParse, A, Z);
 }
@@ -1657,8 +1657,14 @@ windowdefn(A) ::= nm(X) AS LP window(Y) RP. {
 %type part_opt {ExprList*}
 %destructor part_opt {sqlite3ExprListDelete(pParse->db, $$);}
 
-%type filter_opt {Expr*}
-%destructor filter_opt {sqlite3ExprDelete(pParse->db, $$);}
+%type filter_clause {Expr*}
+%destructor filter_clause {sqlite3ExprDelete(pParse->db, $$);}
+
+%type over_clause {Window*}
+%destructor over_clause {sqlite3WindowDelete(pParse->db, $$);}
+
+%type filter_over {Window*}
+%destructor filter_over {sqlite3WindowDelete(pParse->db, $$);}
 
 %type range_or_rows {int}
 
@@ -1724,25 +1730,33 @@ frame_exclude(A) ::= GROUP|TIES(X).  {A = @X; /*A-overwrites-X*/}
 %destructor window_clause {sqlite3WindowListDelete(pParse->db, $$);}
 window_clause(A) ::= WINDOW windowdefn_list(B). { A = B; }
 
-%type over_clause {Window*}
-%destructor over_clause {sqlite3WindowDelete(pParse->db, $$);}
-over_clause(A) ::= filter_opt(W) OVER LP window(Z) RP. {
+filter_over(A) ::= filter_clause(F) over_clause(O). {
+  O->pFilter = F;
+  A = O;
+}
+filter_over(A) ::= over_clause(O). {
+  A = O;
+}
+filter_over(A) ::= filter_clause(F). {
+  A = (Window*)sqlite3DbMallocZero(pParse->db, sizeof(Window));
+  if( A ){
+    A->eFrmType = TK_FILTER;
+    A->pFilter = F;
+  }
+}
+
+over_clause(A) ::= OVER LP window(Z) RP. {
   A = Z;
   assert( A!=0 );
-  A->pFilter = W;
 }
-over_clause(A) ::= filter_opt(W) OVER nm(Z). {
+over_clause(A) ::= OVER nm(Z). {
   A = (Window*)sqlite3DbMallocZero(pParse->db, sizeof(Window));
   if( A ){
     A->zName = sqlite3DbStrNDup(pParse->db, Z.z, Z.n);
-    A->pFilter = W;
-  }else{
-    sqlite3ExprDelete(pParse->db, W);
   }
 }
 
-filter_opt(A) ::= .                            { A = 0; }
-filter_opt(A) ::= FILTER LP WHERE expr(X) RP.  { A = X; }
+filter_clause(A) ::= FILTER LP WHERE expr(X) RP.  { A = X; }
 %endif /* SQLITE_OMIT_WINDOWFUNC */
 
 /*
diff --git a/src/prepare.c b/src/prepare.c
index 3f1a79b14..f385c1fc7 100644
--- a/src/prepare.c
+++ b/src/prepare.c
@@ -635,7 +635,7 @@ static int sqlite3Prepare(
   rc = sParse.rc;
 
 #ifndef SQLITE_OMIT_EXPLAIN
-  if( rc==SQLITE_OK && sParse.pVdbe && sParse.explain ){
+  if( sParse.explain && rc==SQLITE_OK && sParse.pVdbe ){
     static const char * const azColName[] = {
        "addr", "opcode", "p1", "p2", "p3", "p4", "p5", "comment",
        "id", "parent", "notused", "detail"
@@ -660,8 +660,8 @@ static int sqlite3Prepare(
   if( db->init.busy==0 ){
     sqlite3VdbeSetSql(sParse.pVdbe, zSql, (int)(sParse.zTail-zSql), prepFlags);
   }
-  if( sParse.pVdbe && (rc!=SQLITE_OK || db->mallocFailed) ){
-    sqlite3VdbeFinalize(sParse.pVdbe);
+  if( rc!=SQLITE_OK || db->mallocFailed ){
+    if( sParse.pVdbe ) sqlite3VdbeFinalize(sParse.pVdbe);
     assert(!(*ppStmt));
   }else{
     *ppStmt = (sqlite3_stmt*)sParse.pVdbe;
diff --git a/src/resolve.c b/src/resolve.c
index 8dac077ee..872d04f57 100644
--- a/src/resolve.c
+++ b/src/resolve.c
@@ -749,7 +749,9 @@ static int resolveExprStep(Walker *pWalker, Expr *pExpr){
       FuncDef *pDef;              /* Information about the function */
       u8 enc = ENC(pParse->db);   /* The database encoding */
       int savedAllowFlags = (pNC->ncFlags & (NC_AllowAgg | NC_AllowWin));
-
+#ifndef SQLITE_OMIT_WINDOWFUNC
+      Window *pWin = (IsWindowFunc(pExpr) ? pExpr->y.pWin : 0);
+#endif
       assert( !ExprHasProperty(pExpr, EP_xIsSelect) );
       zId = pExpr->u.zToken;
       nId = sqlite3Strlen30(zId);
@@ -830,18 +832,18 @@ static int resolveExprStep(Walker *pWalker, Expr *pExpr){
           || (pDef->xValue==0 && pDef->xInverse==0)
           || (pDef->xValue && pDef->xInverse && pDef->xSFunc && pDef->xFinalize)
         );
-        if( pDef && pDef->xValue==0 && ExprHasProperty(pExpr, EP_WinFunc) ){
+        if( pDef && pDef->xValue==0 && pWin ){
           sqlite3ErrorMsg(pParse, 
               "%.*s() may not be used as a window function", nId, zId
           );
           pNC->nErr++;
         }else if( 
               (is_agg && (pNC->ncFlags & NC_AllowAgg)==0)
-           || (is_agg && (pDef->funcFlags&SQLITE_FUNC_WINDOW) && !pExpr->y.pWin)
-           || (is_agg && pExpr->y.pWin && (pNC->ncFlags & NC_AllowWin)==0)
+           || (is_agg && (pDef->funcFlags&SQLITE_FUNC_WINDOW) && !pWin)
+           || (is_agg && pWin && (pNC->ncFlags & NC_AllowWin)==0)
         ){
           const char *zType;
-          if( (pDef->funcFlags & SQLITE_FUNC_WINDOW) || pExpr->y.pWin ){
+          if( (pDef->funcFlags & SQLITE_FUNC_WINDOW) || pWin ){
             zType = "window";
           }else{
             zType = "aggregate";
@@ -849,6 +851,13 @@ static int resolveExprStep(Walker *pWalker, Expr *pExpr){
           sqlite3ErrorMsg(pParse, "misuse of %s function %.*s()",zType,nId,zId);
           pNC->nErr++;
           is_agg = 0;
+        }else if( is_agg==0 && ExprHasProperty(pExpr, EP_WinFunc) ){
+          assert( !IsWindowFunc(pExpr) );
+          sqlite3ErrorMsg(pParse, 
+              "filter clause may not be used with non-aggregate %.*s()", 
+              nId, zId
+          );
+          pNC->nErr++;
         }
 #else
         if( (is_agg && (pNC->ncFlags & NC_AllowAgg)==0) ){
@@ -874,7 +883,7 @@ static int resolveExprStep(Walker *pWalker, Expr *pExpr){
           ** Or arguments of other window functions. But aggregate functions
           ** may be arguments for window functions.  */
 #ifndef SQLITE_OMIT_WINDOWFUNC
-          pNC->ncFlags &= ~(NC_AllowWin | (!pExpr->y.pWin ? NC_AllowAgg : 0));
+          pNC->ncFlags &= ~(NC_AllowWin | (!pWin ? NC_AllowAgg : 0));
 #else
           pNC->ncFlags &= ~NC_AllowAgg;
 #endif
@@ -883,16 +892,16 @@ static int resolveExprStep(Walker *pWalker, Expr *pExpr){
       sqlite3WalkExprList(pWalker, pList);
       if( is_agg ){
 #ifndef SQLITE_OMIT_WINDOWFUNC
-        if( pExpr->y.pWin ){
+        if( pWin ){
           Select *pSel = pNC->pWinSelect;
           if( IN_RENAME_OBJECT==0 ){
-            sqlite3WindowUpdate(pParse, pSel->pWinDefn, pExpr->y.pWin, pDef);
+            sqlite3WindowUpdate(pParse, pSel->pWinDefn, pWin, pDef);
           }
-          sqlite3WalkExprList(pWalker, pExpr->y.pWin->pPartition);
-          sqlite3WalkExprList(pWalker, pExpr->y.pWin->pOrderBy);
-          sqlite3WalkExpr(pWalker, pExpr->y.pWin->pFilter);
+          sqlite3WalkExprList(pWalker, pWin->pPartition);
+          sqlite3WalkExprList(pWalker, pWin->pOrderBy);
+          sqlite3WalkExpr(pWalker, pWin->pFilter);
           if( 0==pSel->pWin 
-           || 0==sqlite3WindowCompare(pParse, pSel->pWin, pExpr->y.pWin) 
+           || 0==sqlite3WindowCompare(pParse, pSel->pWin, pWin, 0)
           ){
             pExpr->y.pWin->pNextWin = pSel->pWin;
             pSel->pWin = pExpr->y.pWin;
@@ -904,6 +913,11 @@ static int resolveExprStep(Walker *pWalker, Expr *pExpr){
           NameContext *pNC2 = pNC;
           pExpr->op = TK_AGG_FUNCTION;
           pExpr->op2 = 0;
+#ifndef SQLITE_OMIT_WINDOWFUNC
+          if( ExprHasProperty(pExpr, EP_WinFunc) ){
+            sqlite3WalkExpr(pWalker, pExpr->y.pWin->pFilter);
+          }
+#endif
           while( pNC2 && !sqlite3FunctionUsesThisSrc(pExpr, pNC2->pSrcList) ){
             pExpr->op2++;
             pNC2 = pNC2->pNext;
diff --git a/src/select.c b/src/select.c
index 53d33a7ef..dc388b1f7 100644
--- a/src/select.c
+++ b/src/select.c
@@ -4403,7 +4403,10 @@ static u8 minMaxQuery(sqlite3 *db, Expr *pFunc, ExprList **ppMinMax){
 
   assert( *ppMinMax==0 );
   assert( pFunc->op==TK_AGG_FUNCTION );
-  if( pEList==0 || pEList->nExpr!=1 ) return eRet;
+  assert( !IsWindowFunc(pFunc) );
+  if( pEList==0 || pEList->nExpr!=1 || ExprHasProperty(pFunc, EP_WinFunc) ){
+    return eRet;
+  }
   zFunc = pFunc->u.zToken;
   if( sqlite3StrICmp(zFunc, "min")==0 ){
     eRet = WHERE_ORDERBY_MIN;
@@ -4450,7 +4453,7 @@ static Table *isSimpleCount(Select *p, AggInfo *pAggInfo){
   if( pExpr->op!=TK_AGG_FUNCTION ) return 0;
   if( NEVER(pAggInfo->nFunc==0) ) return 0;
   if( (pAggInfo->aFunc[0].pFunc->funcFlags&SQLITE_FUNC_COUNT)==0 ) return 0;
-  if( pExpr->flags&EP_Distinct ) return 0;
+  if( ExprHasProperty(pExpr, EP_Distinct|EP_WinFunc) ) return 0;
 
   return pTab;
 }
@@ -5330,6 +5333,12 @@ static void updateAccumulator(Parse *pParse, int regAcc, AggInfo *pAggInfo){
     int regAgg;
     ExprList *pList = pF->pExpr->x.pList;
     assert( !ExprHasProperty(pF->pExpr, EP_xIsSelect) );
+    assert( !IsWindowFunc(pF->pExpr) );
+    if( ExprHasProperty(pF->pExpr, EP_WinFunc) ){
+      Expr *pFilter = pF->pExpr->y.pWin->pFilter;
+      addrNext = sqlite3VdbeMakeLabel(pParse);
+      sqlite3ExprIfFalse(pParse, pFilter, addrNext, SQLITE_JUMPIFNULL);
+    }
     if( pList ){
       nArg = pList->nExpr;
       regAgg = sqlite3GetTempRange(pParse, nArg);
@@ -5339,7 +5348,9 @@ static void updateAccumulator(Parse *pParse, int regAcc, AggInfo *pAggInfo){
       regAgg = 0;
     }
     if( pF->iDistinct>=0 ){
-      addrNext = sqlite3VdbeMakeLabel(pParse);
+      if( addrNext==0 ){ 
+        addrNext = sqlite3VdbeMakeLabel(pParse);
+      }
       testcase( nArg==0 );  /* Error condition */
       testcase( nArg>1 );   /* Also an error */
       codeDistinct(pParse, pF->iDistinct, addrNext, 1, regAgg);
@@ -6222,9 +6233,16 @@ int sqlite3Select(
       minMaxFlag = WHERE_ORDERBY_NORMAL;
     }
     for(i=0; i<sAggInfo.nFunc; i++){
-      assert( !ExprHasProperty(sAggInfo.aFunc[i].pExpr, EP_xIsSelect) );
+      Expr *pExpr = sAggInfo.aFunc[i].pExpr;
+      assert( !ExprHasProperty(pExpr, EP_xIsSelect) );
       sNC.ncFlags |= NC_InAggFunc;
-      sqlite3ExprAnalyzeAggList(&sNC, sAggInfo.aFunc[i].pExpr->x.pList);
+      sqlite3ExprAnalyzeAggList(&sNC, pExpr->x.pList);
+#ifndef SQLITE_OMIT_WINDOWFUNC
+      assert( !IsWindowFunc(pExpr) );
+      if( ExprHasProperty(pExpr, EP_WinFunc) ){
+        sqlite3ExprAnalyzeAggregates(&sNC, pExpr->y.pWin->pFilter);
+      }
+#endif
       sNC.ncFlags &= ~NC_InAggFunc;
     }
     sAggInfo.mxReg = pParse->nMem;
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 1c4618331..c123dfffb 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -2491,7 +2491,7 @@ struct Expr {
   union {
     Table *pTab;           /* TK_COLUMN: Table containing column. Can be NULL
                            ** for a column of an index on an expression */
-    Window *pWin;          /* TK_FUNCTION: Window definition for the func */
+    Window *pWin;          /* EP_WinFunc: Window/Filter defn for a function */
     struct {               /* TK_IN, TK_SELECT, and TK_EXISTS */
       int iAddr;             /* Subroutine entry address */
       int regReturn;         /* Register used to hold return address */
@@ -2580,6 +2580,14 @@ struct Expr {
 #define EXPRDUP_REDUCE         0x0001  /* Used reduced-size Expr nodes */
 
 /*
+** True if the expression passed as an argument was a function with
+** an OVER() clause (a window function).
+*/
+#define IsWindowFunc(p) ( \
+    ExprHasProperty((p), EP_WinFunc) && p->y.pWin->eFrmType!=TK_FILTER \
+)
+
+/*
 ** A list of expressions.  Each expression may optionally have a
 ** name.  An expr/name combination can be used in several ways, such
 ** as the list of "expr AS ID" fields following a "SELECT" or in the
@@ -3552,10 +3560,11 @@ struct TreeView {
 #endif /* SQLITE_DEBUG */
 
 /*
-** This object is used in various ways, all related to window functions
+** This object is used in various ways, most (but not all) related to window
+** functions.
 **
 **   (1) A single instance of this structure is attached to the
-**       the Expr.pWin field for each window function in an expression tree.
+**       the Expr.y.pWin field for each window function in an expression tree.
 **       This object holds the information contained in the OVER clause,
 **       plus additional fields used during code generation.
 **
@@ -3566,6 +3575,10 @@ struct TreeView {
 **   (3) The terms of the WINDOW clause of a SELECT are instances of this
 **       object on a linked list attached to Select.pWinDefn.
 **
+**   (4) For an aggregate function with a FILTER clause, an instance
+**       of this object is stored in Expr.y.pWin with eFrmType set to
+**       TK_FILTER. In this case the only field used is Window.pFilter.
+**
 ** The uses (1) and (2) are really the same Window object that just happens
 ** to be accessible in two different ways.  Use case (3) are separate objects.
 */
@@ -3603,7 +3616,7 @@ void sqlite3WindowDelete(sqlite3*, Window*);
 void sqlite3WindowListDelete(sqlite3 *db, Window *p);
 Window *sqlite3WindowAlloc(Parse*, int, int, Expr*, int , Expr*, u8);
 void sqlite3WindowAttach(Parse*, Expr*, Window*);
-int sqlite3WindowCompare(Parse*, Window*, Window*);
+int sqlite3WindowCompare(Parse*, Window*, Window*, int);
 void sqlite3WindowCodeInit(Parse*, Window*);
 void sqlite3WindowCodeStep(Parse*, Select*, WhereInfo*, int, int);
 int sqlite3WindowRewrite(Parse*, Select*);
diff --git a/src/vdbeaux.c b/src/vdbeaux.c
index c21d7db40..5781d8f21 100644
--- a/src/vdbeaux.c
+++ b/src/vdbeaux.c
@@ -4607,7 +4607,11 @@ static int vdbeRecordCompareString(
     nCmp = MIN( pPKey2->aMem[0].n, nStr );
     res = memcmp(&aKey1[szHdr], pPKey2->aMem[0].z, nCmp);
 
-    if( res==0 ){
+    if( res>0 ){
+      res = pPKey2->r2;
+    }else if( res<0 ){
+      res = pPKey2->r1;
+    }else{
       res = nStr - pPKey2->aMem[0].n;
       if( res==0 ){
         if( pPKey2->nField>1 ){
@@ -4621,10 +4625,6 @@ static int vdbeRecordCompareString(
       }else{
         res = pPKey2->r1;
       }
-    }else if( res>0 ){
-      res = pPKey2->r2;
-    }else{
-      res = pPKey2->r1;
     }
   }
 
diff --git a/src/walker.c b/src/walker.c
index eff358525..b976886c5 100644
--- a/src/walker.c
+++ b/src/walker.c
@@ -63,18 +63,22 @@ static SQLITE_NOINLINE int walkExpr(Walker *pWalker, Expr *pExpr){
       if( pExpr->pLeft && walkExpr(pWalker, pExpr->pLeft) ) return WRC_Abort;
        assert( pExpr->x.pList==0 || pExpr->pRight==0 );
       if( pExpr->pRight ){
+        assert( !ExprHasProperty(pExpr, EP_WinFunc) );
         pExpr = pExpr->pRight;
         continue;
       }else if( ExprHasProperty(pExpr, EP_xIsSelect) ){
+        assert( !ExprHasProperty(pExpr, EP_WinFunc) );
         if( sqlite3WalkSelect(pWalker, pExpr->x.pSelect) ) return WRC_Abort;
-      }else if( pExpr->x.pList ){
-        if( sqlite3WalkExprList(pWalker, pExpr->x.pList) ) return WRC_Abort;
-      }
+      }else{
+        if( pExpr->x.pList ){
+          if( sqlite3WalkExprList(pWalker, pExpr->x.pList) ) return WRC_Abort;
+        }
 #ifndef SQLITE_OMIT_WINDOWFUNC
-      if( ExprHasProperty(pExpr, EP_WinFunc) ){
-        if( walkWindowList(pWalker, pExpr->y.pWin) ) return WRC_Abort;
-      }
+        if( ExprHasProperty(pExpr, EP_WinFunc) ){
+          if( walkWindowList(pWalker, pExpr->y.pWin) ) return WRC_Abort;
+        }
 #endif
+      }
     }
     break;
   }
diff --git a/src/window.c b/src/window.c
index dcd7107a4..ed39107b9 100644
--- a/src/window.c
+++ b/src/window.c
@@ -1196,17 +1196,14 @@ void sqlite3WindowChain(Parse *pParse, Window *pWin, Window *pList){
 void sqlite3WindowAttach(Parse *pParse, Expr *p, Window *pWin){
   if( p ){
     assert( p->op==TK_FUNCTION );
-    /* This routine is only called for the parser.  If pWin was not
-    ** allocated due to an OOM, then the parser would fail before ever
-    ** invoking this routine */
-    if( ALWAYS(pWin) ){
-      p->y.pWin = pWin;
-      ExprSetProperty(p, EP_WinFunc);
-      pWin->pOwner = p;
-      if( p->flags & EP_Distinct ){
-        sqlite3ErrorMsg(pParse,
-           "DISTINCT is not supported for window functions");
-      }
+    assert( pWin );
+    p->y.pWin = pWin;
+    ExprSetProperty(p, EP_WinFunc);
+    pWin->pOwner = p;
+    if( (p->flags & EP_Distinct) && pWin->eFrmType!=TK_FILTER ){
+      sqlite3ErrorMsg(pParse,
+          "DISTINCT is not supported for window functions"
+      );
     }
   }else{
     sqlite3WindowDelete(pParse->db, pWin);
@@ -1217,7 +1214,7 @@ void sqlite3WindowAttach(Parse *pParse, Expr *p, Window *pWin){
 ** Return 0 if the two window objects are identical, or non-zero otherwise.
 ** Identical window objects can be processed in a single scan.
 */
-int sqlite3WindowCompare(Parse *pParse, Window *p1, Window *p2){
+int sqlite3WindowCompare(Parse *pParse, Window *p1, Window *p2, int bFilter){
   if( p1->eFrmType!=p2->eFrmType ) return 1;
   if( p1->eStart!=p2->eStart ) return 1;
   if( p1->eEnd!=p2->eEnd ) return 1;
@@ -1226,6 +1223,9 @@ int sqlite3WindowCompare(Parse *pParse, Window *p1, Window *p2){
   if( sqlite3ExprCompare(pParse, p1->pEnd, p2->pEnd, -1) ) return 1;
   if( sqlite3ExprListCompare(p1->pPartition, p2->pPartition, -1) ) return 1;
   if( sqlite3ExprListCompare(p1->pOrderBy, p2->pOrderBy, -1) ) return 1;
+  if( bFilter ){
+    if( sqlite3ExprCompare(pParse, p1->pFilter, p2->pFilter, -1) ) return 1;
+  }
   return 0;
 }