Index: src/expr.c
==================================================================
--- src/expr.c
+++ src/expr.c
@@ -1391,11 +1391,12 @@
     case TK_FLOAT:
     case TK_BLOB:
       return 0;
     case TK_COLUMN:
       assert( p->pTab!=0 );
-      return p->iColumn>=0 && p->pTab->aCol[p->iColumn].notNull==0;
+      return ExprHasProperty(p, EP_CanBeNull) ||
+             (p->iColumn>=0 && p->pTab->aCol[p->iColumn].notNull==0);
     default:
       return 1;
   }
 }
 

Index: src/resolve.c
==================================================================
--- src/resolve.c
+++ src/resolve.c
@@ -318,10 +318,14 @@
         }
       }
       if( pMatch ){
         pExpr->iTable = pMatch->iCursor;
         pExpr->pTab = pMatch->pTab;
+        assert( (pMatch->jointype & JT_RIGHT)==0 ); /* RIGHT JOIN not (yet) supported */
+        if( (pMatch->jointype & JT_LEFT)!=0 ){
+          ExprSetProperty(pExpr, EP_CanBeNull);
+        }
         pSchema = pExpr->pTab->pSchema;
       }
     } /* if( pSrcList ) */
 
 #ifndef SQLITE_OMIT_TRIGGER

Index: src/sqliteInt.h
==================================================================
--- src/sqliteInt.h
+++ src/sqliteInt.h
@@ -2012,11 +2012,11 @@
 };
 
 /*
 ** The following are the meanings of bits in the Expr.flags field.
 */
-#define EP_FromJoin  0x000001 /* Originated in ON or USING clause of a join */
+#define EP_FromJoin  0x000001 /* Originates in ON/USING clause of outer join */
 #define EP_Agg       0x000002 /* Contains one or more aggregate functions */
 #define EP_Resolved  0x000004 /* IDs have been resolved to COLUMNs */
 #define EP_Error     0x000008 /* Expression contains one or more errors */
 #define EP_Distinct  0x000010 /* Aggregate function with DISTINCT keyword */
 #define EP_VarSelect 0x000020 /* pSelect is correlated, not constant */
@@ -2032,10 +2032,11 @@
 #define EP_Static    0x008000 /* Held in memory not obtained from malloc() */
 #define EP_MemToken  0x010000 /* Need to sqlite3DbFree() Expr.zToken */
 #define EP_NoReduce  0x020000 /* Cannot EXPRDUP_REDUCE this Expr */
 #define EP_Unlikely  0x040000 /* unlikely() or likelihood() function */
 #define EP_Constant  0x080000 /* Node is a constant */
+#define EP_CanBeNull 0x100000 /* Can be null despite NOT NULL constraint */
 
 /*
 ** These macros can be used to test, set, or clear bits in the 
 ** Expr.flags field.
 */

Index: test/join5.test
==================================================================
--- test/join5.test
+++ test/join5.test
@@ -104,7 +104,61 @@
 } {}
 do_test join5-2.12 {
   execsql {SELECT * FROM xy LEFT JOIN ab ON NULL WHERE NULL}
 } {}
 
+# Ticket https://www.sqlite.org/src/tktview/6f2222d550f5b0ee7ed37601
+# Incorrect output on a LEFT JOIN.
+#
+do_execsql_test join5-3.1 {
+  DROP TABLE IF EXISTS t1;
+  DROP TABLE IF EXISTS t2;
+  DROP TABLE IF EXISTS t3;
+  CREATE TABLE x1(a);
+  INSERT INTO x1 VALUES(1);
+  CREATE TABLE x2(b NOT NULL);
+  CREATE TABLE x3(c, d);
+  INSERT INTO x3 VALUES('a', NULL);
+  INSERT INTO x3 VALUES('b', NULL);
+  INSERT INTO x3 VALUES('c', NULL);
+  SELECT * FROM x1 LEFT JOIN x2 LEFT JOIN x3 ON x3.d = x2.b;
+} {1 {} {} {}}
+do_execsql_test join5-3.2 {
+  DROP TABLE IF EXISTS t1;
+  DROP TABLE IF EXISTS t2;
+  DROP TABLE IF EXISTS t3;
+  DROP TABLE IF EXISTS t4;
+  DROP TABLE IF EXISTS t5;
+  CREATE TABLE t1(x text NOT NULL, y text);
+  CREATE TABLE t2(u text NOT NULL, x text NOT NULL);
+  CREATE TABLE t3(w text NOT NULL, v text);
+  CREATE TABLE t4(w text NOT NULL, z text NOT NULL);
+  CREATE TABLE t5(z text NOT NULL, m text);
+  INSERT INTO t1 VALUES('f6d7661f-4efe-4c90-87b5-858e61cd178b',NULL);
+  INSERT INTO t1 VALUES('f6ea82c3-2cad-45ce-ae8f-3ddca4fb2f48',NULL);
+  INSERT INTO t1 VALUES('f6f47499-ecb4-474b-9a02-35be73c235e5',NULL);
+  INSERT INTO t1 VALUES('56f47499-ecb4-474b-9a02-35be73c235e5',NULL);
+  INSERT INTO t3 VALUES('007f2033-cb20-494c-b135-a1e4eb66130c',
+                        'f6d7661f-4efe-4c90-87b5-858e61cd178b');
+  SELECT *
+    FROM t3
+         INNER JOIN t1 ON t1.x= t3.v AND t1.y IS NULL
+         LEFT JOIN t4  ON t4.w = t3.w
+         LEFT JOIN t5  ON t5.z = t4.z
+         LEFT JOIN t2  ON t2.u = t5.m
+         LEFT JOIN t1 xyz ON xyz.y = t2.x;
+} {007f2033-cb20-494c-b135-a1e4eb66130c f6d7661f-4efe-4c90-87b5-858e61cd178b f6d7661f-4efe-4c90-87b5-858e61cd178b {} {} {} {} {} {} {} {} {}}
+do_execsql_test join5-3.3 {
+  DROP TABLE IF EXISTS x1;
+  DROP TABLE IF EXISTS x2;
+  DROP TABLE IF EXISTS x3;
+  CREATE TABLE x1(a);
+  INSERT INTO x1 VALUES(1);
+  CREATE TABLE x2(b NOT NULL);
+  CREATE TABLE x3(c, d);
+  INSERT INTO x3 VALUES('a', NULL);
+  INSERT INTO x3 VALUES('b', NULL);
+  INSERT INTO x3 VALUES('c', NULL);
+  SELECT * FROM x1 LEFT JOIN x2 JOIN x3 WHERE x3.d = x2.b;
+} {}
 
 finish_test