Index: src/func.c
==================================================================
--- src/func.c
+++ src/func.c
@@ -1663,11 +1663,11 @@
   if( sqlite3_value_type(argv[0])==SQLITE_NULL ) return;
   pAccum = (StrAccum*)sqlite3_aggregate_context(context, sizeof(*pAccum));
 
   if( pAccum ){
     sqlite3 *db = sqlite3_context_db_handle(context);
-    int firstTerm = pAccum->mxAlloc==0;
+    int firstTerm = pAccum->nChar==0;
     pAccum->mxAlloc = db->aLimit[SQLITE_LIMIT_LENGTH];
     if( !firstTerm ){
       if( argc==2 ){
         zSep = (char*)sqlite3_value_text(argv[1]);
         nSep = sqlite3_value_bytes(argv[1]);
@@ -1679,10 +1679,33 @@
     }
     zVal = (char*)sqlite3_value_text(argv[0]);
     nVal = sqlite3_value_bytes(argv[0]);
     if( zVal ) sqlite3_str_append(pAccum, zVal, nVal);
   }
+}
+static void groupConcatInverse(
+  sqlite3_context *context,
+  int argc,
+  sqlite3_value **argv
+){
+  int n;
+  assert( argc==1 || argc==2 );
+  StrAccum *pAccum;
+  if( sqlite3_value_type(argv[0])==SQLITE_NULL ) return;
+  pAccum = (StrAccum*)sqlite3_aggregate_context(context, sizeof(*pAccum));
+  if( pAccum ){
+    n = sqlite3_value_bytes(argv[0]);
+    if( argc==2 ){
+      n += sqlite3_value_bytes(argv[1]);
+    }
+    if( n>=pAccum->nChar ){
+      pAccum->nChar = 0;
+    }else{
+      pAccum->nChar -= n;
+      memmove(pAccum->zText, &pAccum->zText[n], pAccum->nChar);
+    }
+  }
 }
 static void groupConcatFinalize(sqlite3_context *context){
   StrAccum *pAccum;
   pAccum = sqlite3_aggregate_context(context, 0);
   if( pAccum ){
@@ -1892,20 +1915,19 @@
     VFUNCTION(total_changes,     0, 0, 0, total_changes    ),
     FUNCTION(replace,            3, 0, 0, replaceFunc      ),
     FUNCTION(zeroblob,           1, 0, 0, zeroblobFunc     ),
     FUNCTION(substr,             2, 0, 0, substrFunc       ),
     FUNCTION(substr,             3, 0, 0, substrFunc       ),
-    WAGGREGATE(sum,        1, 0, 0, sumStep, sumInverse,   sumFinalize),
-    WAGGREGATE(total,      1, 0, 0, sumStep, sumInverse,   totalFinalize    ),
-    WAGGREGATE(avg,        1, 0, 0, sumStep, sumInverse,   avgFinalize    ),
-    AGGREGATE2(count,            0, 0, 0, countStep,       countFinalize,
-               SQLITE_FUNC_COUNT  ),
-    WAGGREGATE(count,             1, 0, 0, countStep, 0,    countFinalize  ),
-    AGGREGATE(group_concat,      1, 0, 0, groupConcatStep, groupConcatFinalize,
-        groupConcatValue),
-    AGGREGATE(group_concat,      2, 0, 0, groupConcatStep, groupConcatFinalize,
-        groupConcatValue),
+    WAGGREGATE(sum,   1,0,0, sumStep, sumFinalize, sumFinalize, sumInverse),
+    WAGGREGATE(total, 1,0,0, sumStep, totalFinalize, totalFinalize, sumInverse),
+    WAGGREGATE(avg,   1,0,0, sumStep, avgFinalize, avgFinalize, sumInverse),
+    AGGREGATE2(count, 0,0,0, countStep, countFinalize, SQLITE_FUNC_COUNT  ),
+    WAGGREGATE(count, 1,0,0, countStep, countFinalize, 0, 0 ),
+    WAGGREGATE(group_concat, 1, 0, 0, groupConcatStep, 
+        groupConcatFinalize, groupConcatValue, groupConcatInverse),
+    WAGGREGATE(group_concat, 2, 0, 0, groupConcatStep, 
+        groupConcatFinalize, groupConcatValue, groupConcatInverse),
   
     LIKEFUNC(glob, 2, &globInfo, SQLITE_FUNC_LIKE|SQLITE_FUNC_CASE),
 #ifdef SQLITE_CASE_SENSITIVE_LIKE
     LIKEFUNC(like, 2, &likeInfoAlt, SQLITE_FUNC_LIKE|SQLITE_FUNC_CASE),
     LIKEFUNC(like, 3, &likeInfoAlt, SQLITE_FUNC_LIKE|SQLITE_FUNC_CASE),

Index: src/sqliteInt.h
==================================================================
--- src/sqliteInt.h
+++ src/sqliteInt.h
@@ -1723,13 +1723,13 @@
    SQLITE_INT_TO_PTR(arg), 0, xStep,xFinal,xValue,0,#zName, {0}}
 #define AGGREGATE2(zName, nArg, arg, nc, xStep, xFinal, extraFlags) \
   {nArg, SQLITE_UTF8|(nc*SQLITE_FUNC_NEEDCOLL)|extraFlags, \
    SQLITE_INT_TO_PTR(arg), 0, xStep,xFinal,xFinal,0,#zName, {0}}
 
-#define WAGGREGATE(zName, nArg, arg, nc, xStep, xInverse, xFinal) \
+#define WAGGREGATE(zName, nArg, arg, nc, xStep, xFinal, xValue, xInverse) \
   {nArg, SQLITE_UTF8|(nc*SQLITE_FUNC_NEEDCOLL), \
-   SQLITE_INT_TO_PTR(arg), 0, xStep,xFinal,xFinal,xInverse,#zName, {0}}
+   SQLITE_INT_TO_PTR(arg), 0, xStep,xFinal,xValue,xInverse,#zName, {0}}
 
 /*
 ** All current savepoints are stored in a linked list starting at
 ** sqlite3.pSavepoint. The first element in the list is the most recently
 ** opened savepoint. Savepoints are added to the list by the vdbe

Index: test/pg_common.tcl
==================================================================
--- test/pg_common.tcl
+++ test/pg_common.tcl
@@ -58,10 +58,11 @@
   set ret
 }
 
 proc execsql_test {tn sql} {
   set res [execsql $sql]
+  set sql [string map {string_agg group_concat} $sql]
   puts $::fd "do_execsql_test $tn {"
   puts $::fd "  [string trim $sql]"
   puts $::fd "} {$res}"
   puts $::fd ""
 }

Index: test/window3.tcl
==================================================================
--- test/window3.tcl
+++ test/window3.tcl
@@ -278,9 +278,29 @@
     SELECT lag(b,b) OVER ( ORDER BY b%10,a $window ) FROM t2
   "
   execsql_test 1.$tn.13.6 "
     SELECT lag(b,b) OVER (PARTITION BY b%2,a ORDER BY b%10 $window) FROM t2
   "
+
+  execsql_test 1.$tn.14.1 "
+    SELECT string_agg(CAST(b AS TEXT), '.') OVER (ORDER BY a $window) FROM t2
+  "
+
+  execsql_test 1.$tn.14.2 "
+    SELECT string_agg(CAST(b AS TEXT), '.') OVER (PARTITION BY b%10 ORDER BY a $window) FROM t2
+  "
+  execsql_test 1.$tn.14.3 "
+    SELECT string_agg(CAST(b AS TEXT), '.') OVER ( ORDER BY b,a $window ) FROM t2
+  "
+  execsql_test 1.$tn.14.4 "
+    SELECT string_agg(CAST(b AS TEXT), '.') OVER ( PARTITION BY b%10 ORDER BY b,a $window ) FROM t2
+  "
+  execsql_test 1.$tn.14.5 "
+    SELECT string_agg(CAST(b AS TEXT), '.') OVER ( ORDER BY b%10,a $window ) FROM t2
+  "
+  execsql_test 1.$tn.14.6 "
+    SELECT string_agg(CAST(b AS TEXT), '.') OVER (PARTITION BY b%2,a ORDER BY b%10 $window) FROM t2
+  "
 }
 
 finish_test
 

Index: test/window3.test
==================================================================
--- test/window3.test
+++ test/window3.test
cannot compute difference between binary files

Index: test/window4.tcl
==================================================================
--- test/window4.tcl
+++ test/window4.tcl
@@ -63,10 +63,16 @@
   SELECT a, lag(b, 2) OVER (ORDER BY a) FROM t4
 }
 execsql_test 2.3.3 {
   SELECT a, lag(b, 3, 'abc') OVER (ORDER BY a) FROM t4
 }
+
+execsql_test 2.4.1 {
+  SELECT string_agg(b, '.') OVER (
+    ORDER BY a ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING
+  ) FROM t4
+}
 
 execsql_test 3.0 {
   DROP TABLE IF EXISTS t5;
   CREATE TABLE t5(a INTEGER PRIMARY KEY, b TEXT, c TEXT, d INTEGER);
   INSERT INTO t5 VALUES(1, 'A', 'one',   5);

Index: test/window4.test
==================================================================
--- test/window4.test
+++ test/window4.test
@@ -143,10 +143,16 @@
 
 do_execsql_test 2.3.3 {
   SELECT a, lag(b, 3, 'abc') OVER (ORDER BY a) FROM t4
 } {1 abc   2 abc   3 abc   4 A   5 B   6 C   7 D   8 E   9 F   10 G}
 
+do_execsql_test 2.4.1 {
+  SELECT group_concat(b, '.') OVER (
+    ORDER BY a ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING
+  ) FROM t4
+} {A.B.C.D.E.F.G.H.I.J   B.C.D.E.F.G.H.I.J   C.D.E.F.G.H.I.J   D.E.F.G.H.I.J   E.F.G.H.I.J   F.G.H.I.J   G.H.I.J   H.I.J   I.J   J}
+
 do_execsql_test 3.0 {
   DROP TABLE IF EXISTS t5;
   CREATE TABLE t5(a INTEGER PRIMARY KEY, b TEXT, c TEXT, d INTEGER);
   INSERT INTO t5 VALUES(1, 'A', 'one',   5);
   INSERT INTO t5 VALUES(2, 'B', 'two',   4);