Subject: [PATCH] When rewriting a query for window functions, if the rewrite 
changes the depth of TK_AGG_FUNCTION nodes, be sure to adjust the Expr.op2 
field appropriately.

diff --git a/src/resolve.c b/src/resolve.c
index cdcf4d9..c47f6bb 100644
--- a/src/resolve.c
+++ b/src/resolve.c
@@ -24,6 +24,8 @@
 **
 ** incrAggFunctionDepth(pExpr,n) is the main routine.  incrAggDepth(..)
 ** is a helper function - a callback for the tree walker.
+**
+** See also the sqlite3WindowExtraAggFuncDepth() routine in window.c
 */
 static int incrAggDepth(Walker *pWalker, Expr *pExpr){
   if( pExpr->op==TK_AGG_FUNCTION ) pExpr->op2 += pWalker->u.n;
diff --git a/src/select.c b/src/select.c
index a6d1757..6f5570c 100644
--- a/src/select.c
+++ b/src/select.c
@@ -1961,7 +1961,7 @@ int sqlite3ColumnsFromExprList(
         assert( pColExpr!=0 );
       }
       assert( pColExpr->op!=TK_AGG_COLUMN );
-      if( pColExpr->op==TK_COLUMN ){
+      if( pColExpr->op==TK_COLUMN && pColExpr->y.pTab ){
         /* For columns use the column name name */
         int iCol = pColExpr->iColumn;
         Table *pTab = pColExpr->y.pTab;
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 1cf6937..ea9a7ae 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -3579,6 +3579,8 @@ void sqlite3WindowUpdate(Parse*, Window*, Window*, FuncDef*);
 Window *sqlite3WindowDup(sqlite3 *db, Expr *pOwner, Window *p);
 Window *sqlite3WindowListDup(sqlite3 *db, Window *p);
 void sqlite3WindowFunctions(void);
+int sqlite3WalkerDepthIncrease(Walker*,Select*);
+void sqlite3WalkerDepthDecrease(Walker*,Select*);
 #else
 # define sqlite3WindowDelete(a,b)
 # define sqlite3WindowFunctions()
diff --git a/src/walker.c b/src/walker.c
index c31d94f..8cd3b65 100644
--- a/src/walker.c
+++ b/src/walker.c
@@ -165,3 +165,16 @@ int sqlite3WalkSelect(Walker *pWalker, Select *p){
   }while( p!=0 );
   return WRC_Continue;
 }
+
+/* Increase the walkerDepth when entering a subquery, and
+** descrease when leaving the subquery.
+*/
+int sqlite3WalkerDepthIncrease(Walker *pWalker, Select *pSelect){
+  UNUSED_PARAMETER(pSelect);
+  pWalker->walkerDepth++;
+  return WRC_Continue;
+}
+void sqlite3WalkerDepthDecrease(Walker *pWalker, Select *pSelect){
+  UNUSED_PARAMETER(pSelect);
+  pWalker->walkerDepth--;
+}
\ No newline at end of file
diff --git a/src/window.c b/src/window.c
index c65eadd..48d8090 100644
--- a/src/window.c
+++ b/src/window.c
@@ -738,6 +738,23 @@ static ExprList *exprListAppendList(
   return pList;
 }
 
+/*
+** When rewriting a query, if the new subquery in the FROM clause
+** contains TK_AGG_FUNCTION nodes that refer to an outer query,
+** then we have to increase the Expr->op2 values of those nodes
+** due to the extra subquery layer that was added.
+**
+** See also the incrAggDepth() routine in resolve.c
+*/
+static int sqlite3WindowExtraAggFuncDepth(Walker *pWalker, Expr *pExpr){
+  if( pExpr->op==TK_AGG_FUNCTION
+   && pExpr->op2>=pWalker->walkerDepth
+  ){
+    pExpr->op2++;
+  }
+  return WRC_Continue;
+}
+
 /*
 ** If the SELECT statement passed as the second argument does not invoke
 ** any SQL window functions, this function is a no-op. Otherwise, it 
@@ -827,14 +844,24 @@ int sqlite3WindowRewrite(Parse *pParse, Select *p){
     p->pSrc = sqlite3SrcListAppend(db, 0, 0, 0);
     assert( p->pSrc || db->mallocFailed );
     if( p->pSrc ){
+      Table *pTab2;
+      Walker w;
       p->pSrc->a[0].pSelect = pSub;
       sqlite3SrcListAssignCursors(pParse, p->pSrc);
-      if( sqlite3ExpandSubquery(pParse, &p->pSrc->a[0]) ){
+      pTab2 = sqlite3ResultSetOfSelect(pParse, pSub);
+      if( pTab2==0 ){
         rc = SQLITE_NOMEM;
       }else{
         pSub->selFlags |= SF_Expanded;
         p->selFlags &= ~SF_Aggregate;
         sqlite3SelectPrep(pParse, pSub, 0);
+        pTab2->tabFlags |= TF_Ephemeral;
+        p->pSrc->a[0].pTab = pTab2;
+        memset(&w, 0, sizeof(w));
+        w.xExprCallback = sqlite3WindowExtraAggFuncDepth;
+        w.xSelectCallback = sqlite3WalkerDepthIncrease;
+        w.xSelectCallback2 = sqlite3WalkerDepthDecrease;
+        sqlite3WalkSelect(&w, pSub);
       }
 
       sqlite3VdbeAddOp2(v, OP_OpenEphemeral, pMWin->iEphCsr, pSublist->nExpr);
diff --git a/test/window1.test b/test/window1.test
index a8399a8..13ecc32 100644
--- a/test/window1.test
+++ b/test/window1.test
@@ -594,4 +594,20 @@ do_execsql_test 13.5 {
 } {
 }
 
+# 2020-05-23
+# ticket 7a5279a25c57adf1
+#
+reset_db
+do_execsql_test 53.0 {
+  CREATE TABLE a(c UNIQUE);
+  INSERT INTO a VALUES(4),(0),(9),(-9);
+  SELECT a.c
+    FROM a
+    JOIN a AS b ON a.c=4
+    JOIN a AS e ON a.c=e.c
+   WHERE a.c=(SELECT (SELECT coalesce(lead(2) OVER(),0) + sum(d.c))
+                FROM a AS d
+               WHERE a.c);
+} {4 4 4 4}
+
 finish_test