diff --git a/_FiveSql2/src/TSqlExecutor.prg b/_FiveSql2/src/TSqlExecutor.prg
index 8db3bab..b5c486f 100644
--- a/_FiveSql2/src/TSqlExecutor.prg
+++ b/_FiveSql2/src/TSqlExecutor.prg
@@ -2955,7 +2955,7 @@ METHOD ApplyWindowFunctions( aRows, aFN, aCols ) CLASS TSqlExecutor
    LOCAL nLagLead, nArgCol, xDefault
    LOCAL nRunSum, nRunCount
    LOCAL aWinCols, nWC
-   LOCAL hFrame, nFS, nFE, m, xVal, xMin, xMax
+   LOCAL hFrame, nFS, nFE, m, xVal, xMin, xMax, lDefaultFrame
 
    /* Scan for window function columns */
    aWinCols := {}
@@ -3114,19 +3114,73 @@ METHOD ApplyWindowFunctions( aRows, aFN, aCols ) CLASS TSqlExecutor
                ENDIF
             ENDIF
 
+            /* Detect default frame (UNBOUNDED PRECEDING to CURRENT ROW)
+             * which can use the O(N) incremental running-sum path instead
+             * of the O(N²) general per-row-frame-aggregate. */
+            /* Default frame = UNBOUNDED PRECEDING to CURRENT ROW.
+             * This covers: no frame spec, or explicit ROWS UNBOUNDED
+             * PRECEDING (without BETWEEN or with implied CURRENT ROW end).
+             * The incremental O(N) path handles this; the general frame
+             * loop is only needed for custom boundaries like
+             * ROWS BETWEEN 6 PRECEDING AND CURRENT ROW. */
+            lDefaultFrame := .T.
+            IF hFrame != NIL .AND. ValType( hFrame ) == "H"
+               IF hb_HHasKey( hFrame, "end" ) .AND. ;
+                  ! ( "CURRENT ROW" $ hFrame[ "end" ] )
+                  lDefaultFrame := .F.
+               ENDIF
+               IF hb_HHasKey( hFrame, "start" ) .AND. ;
+                  ! ( "UNBOUNDED PRECEDING" $ hFrame[ "start" ] )
+                  lDefaultFrame := .F.
+               ENDIF
+            ENDIF
+            IF lDefaultFrame
+               /* O(N) incremental path — original fast code */
+               nRunSum := 0
+               nRunCount := 0
+               xMin := NIL
+               xMax := NIL
+               FOR k := 1 TO Len( aPartIdx )
+                  IF cFunc == "COUNT" .AND. nArgCol == 0
+                     nRunCount++
+                  ELSEIF nArgCol > 0 .AND. nArgCol <= Len( aRows[ aPartIdx[ k ] ] )
+                     xVal := aRows[ aPartIdx[ k ] ][ nArgCol ]
+                     IF xVal != NIL
+                        nRunCount++
+                        nRunSum += SqlCoerceNum( xVal )
+                        IF xMin == NIL .OR. SqlCmpLt( xVal, xMin )
+                           xMin := xVal
+                        ENDIF
+                        IF xMax == NIL .OR. SqlCmpLt( xMax, xVal )
+                           xMax := xVal
+                        ENDIF
+                     ENDIF
+                  ENDIF
+                  IF nColIdx <= Len( aRows[ aPartIdx[ k ] ] )
+                     DO CASE
+                     CASE cFunc == "SUM"
+                        aRows[ aPartIdx[ k ] ][ nColIdx ] := nRunSum
+                     CASE cFunc == "AVG"
+                        aRows[ aPartIdx[ k ] ][ nColIdx ] := iif( nRunCount > 0, nRunSum / nRunCount, NIL )
+                     CASE cFunc == "COUNT"
+                        aRows[ aPartIdx[ k ] ][ nColIdx ] := nRunCount
+                     CASE cFunc == "MIN"
+                        aRows[ aPartIdx[ k ] ][ nColIdx ] := xMin
+                     CASE cFunc == "MAX"
+                        aRows[ aPartIdx[ k ] ][ nColIdx ] := xMax
+                     ENDCASE
+                  ENDIF
+               NEXT
+            ELSE
+            /* General frame path — O(N*W) where W = frame width */
             FOR k := 1 TO Len( aPartIdx )
-               /* Compute frame boundaries for this row */
-               nFS := 1    /* default: UNBOUNDED PRECEDING */
-               nFE := k    /* default: CURRENT ROW */
-               IF hFrame != NIL .AND. ValType( hFrame ) == "H"
-                  IF hb_HHasKey( hFrame, "start" )
-                     nFS := SqlFrameOffset( hFrame[ "start" ], k, Len( aPartIdx ) )
-                  ENDIF
-                  IF hb_HHasKey( hFrame, "end" )
-                     nFE := SqlFrameOffset( hFrame[ "end" ], k, Len( aPartIdx ) )
-                  ELSE
-                     nFE := k
-                  ENDIF
+               nFS := 1
+               nFE := k
+               IF hb_HHasKey( hFrame, "start" )
+                  nFS := SqlFrameOffset( hFrame[ "start" ], k, Len( aPartIdx ) )
+               ENDIF
+               IF hb_HHasKey( hFrame, "end" )
+                  nFE := SqlFrameOffset( hFrame[ "end" ], k, Len( aPartIdx ) )
                ENDIF
                IF nFS < 1
                   nFS := 1
@@ -3135,7 +3189,6 @@ METHOD ApplyWindowFunctions( aRows, aFN, aCols ) CLASS TSqlExecutor
                   nFE := Len( aPartIdx )
                ENDIF
 
-               /* Aggregate over the frame window */
                nRunSum := 0
                nRunCount := 0
                xMin := NIL
@@ -3174,6 +3227,7 @@ METHOD ApplyWindowFunctions( aRows, aFN, aCols ) CLASS TSqlExecutor
                   ENDCASE
                ENDIF
             NEXT
+            ENDIF  /* lDefaultFrame */
 
          ENDCASE
       NEXT