Index: src/select.c
==================================================================
--- src/select.c
+++ src/select.c
@@ -3416,10 +3416,11 @@
   Parse *pParse;            /* The parsing context */
   int iTable;               /* Replace references to this table */
   int iNewTable;            /* New table number */
   int isLeftJoin;           /* Add TK_IF_NULL_ROW opcodes on each replacement */
   ExprList *pEList;         /* Replacement expressions */
+  int bFlattener;           /* True for query-flattener, false otherwise */
 } SubstContext;
 
 /* Forward Declarations */
 static void substExprList(SubstContext*, ExprList*);
 static void substSelect(SubstContext*, Select*, int);
@@ -3476,10 +3477,22 @@
           pNew->iRightJoinTable = pExpr->iRightJoinTable;
           ExprSetProperty(pNew, EP_FromJoin);
         }
         sqlite3ExprDelete(db, pExpr);
         pExpr = pNew;
+
+        /* If this call is part of query-flattening, ensure that the
+        ** new expression has an implicit collation sequence. */
+        if( pSubst->bFlattener && pExpr ){
+          if( pExpr->op!=TK_COLUMN && pExpr->op!=TK_COLLATE ){
+            CollSeq *pColl = sqlite3ExprCollSeq(pSubst->pParse, pExpr);
+            pExpr = sqlite3ExprAddCollateString(pSubst->pParse, pExpr, 
+                (pColl ? pColl->zName : "BINARY")
+            );
+          }
+          ExprClearProperty(pExpr, EP_Collate);
+        }
       }
     }
   }else{
     if( pExpr->op==TK_IF_NULL_ROW && pExpr->iTable==pSubst->iTable ){
       pExpr->iTable = pSubst->iNewTable;
@@ -4041,10 +4054,11 @@
       x.pParse = pParse;
       x.iTable = iParent;
       x.iNewTable = iNewParent;
       x.isLeftJoin = isLeftJoin;
       x.pEList = pSub->pEList;
+      x.bFlattener = 1;
       substSelect(&x, pParent, 0);
     }
   
     /* The flattened query is a compound if either the inner or the
     ** outer query is a compound. */
@@ -4366,10 +4380,11 @@
       x.pParse = pParse;
       x.iTable = iCursor;
       x.iNewTable = iCursor;
       x.isLeftJoin = 0;
       x.pEList = pSubq->pEList;
+      x.bFlattener = 0;
       pNew = substExpr(&x, pNew);
       if( pSubq->selFlags & SF_Aggregate ){
         pSubq->pHaving = sqlite3ExprAnd(pParse, pSubq->pHaving, pNew);
       }else{
         pSubq->pWhere = sqlite3ExprAnd(pParse, pSubq->pWhere, pNew);

ADDED   test/tkt-a7debbe0.test
Index: test/tkt-a7debbe0.test
==================================================================
--- /dev/null
+++ test/tkt-a7debbe0.test
@@ -0,0 +1,103 @@
+# 2019 September 10
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+# This file implements regression tests for SQLite library. In particular,
+# that problems related to ticket a7debbe0ad1 have been fixed.
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix tkt-a7debbe0
+
+foreach tn {1 2} {
+  reset_db
+  if {$tn==1} {
+    # Disable the flattener
+    optimization_control db query-flattener 0
+  } else {
+    # Enable the flattener
+    optimization_control db query-flattener 1
+  }
+
+  do_execsql_test $tn.1.0 {
+    CREATE TABLE t0(xyz INTEGER);
+    INSERT INTO t0(xyz) VALUES(456);
+    CREATE VIEW v2(a, B) AS 
+        SELECT 'a', 'B' COLLATE NOCASE FROM t0;
+    CREATE TABLE t2(a, B COLLATE NOCASE);
+    INSERT INTO t2 VALUES('a', 'B');
+    CREATE VIEW v3(a, B) AS
+        SELECT 'a' COLLATE BINARY, 'B' COLLATE NOCASE FROM t0;
+
+    CREATE VIEW v4(a, B) AS
+        SELECT 'a', +CAST('B' COLLATE NOCASE AS TEXT) FROM t0;
+
+    CREATE VIEW v5(a, B) AS
+        SELECT 'a', ('B' COLLATE NOCASE) || '' FROM t0;
+  }
+
+  # Table t2 and views v2 through v5 should all be equivalent.
+  do_execsql_test $tn.1.1.1 { SELECT a   >= B FROM t2;         } 1
+  do_execsql_test $tn.1.1.2 { SELECT 'a' >= 'B' COLLATE NOCASE } 0
+  do_execsql_test $tn.1.1.3 { SELECT a   >= B FROM v2          } 1
+  do_execsql_test $tn.1.1.4 { SELECT a   >= B FROM v3          } 1
+  do_execsql_test $tn.1.1.5 { SELECT a   >= B FROM v4          } 1
+  do_execsql_test $tn.1.1.6 { SELECT a   >= B FROM v5          } 1
+
+  do_execsql_test $tn.1.2.1 { SELECT B   < a FROM t2           } 0
+  do_execsql_test $tn.1.2.2 { SELECT 'B' COLLATE NOCASE < 'a'  } 0
+  do_execsql_test $tn.1.2.3 { SELECT B   < a FROM v2           } 0
+  do_execsql_test $tn.1.2.4 { SELECT B   < a FROM v3           } 0
+  do_execsql_test $tn.1.2.5 { SELECT a  < B FROM v4           } 0
+  do_execsql_test $tn.1.2.6 { SELECT a  < B FROM v5           } 0
+
+  #-------------------------------------------------------------------------
+  do_execsql_test 2.0 {
+    CREATE TABLE t5(a, b COLLATE NOCASE);
+    INSERT INTO t5 VALUES(1, 'XYZ');
+  }
+
+  # Result should be 0, as column "xyz" from the sub-query has implicit
+  # collation sequence BINARY.
+  do_execsql_test 2.1 {
+    SELECT xyz==b FROM ( SELECT a, 'xyz' AS xyz FROM t5 ), t5;
+  } {0}
+
+  # Result should be 1, as literal 'xyz' has no collation sequence, so
+  # the comparison uses the implicit collation sequence of the RHS - NOCASE.
+  do_execsql_test 2.2 {
+    SELECT 'xyz'==b FROM ( SELECT a, 'xyz' AS xyz FROM t5 ), t5;
+  } {1}
+
+  #-----------------------------------------------------------------------
+  # The test case submitted with the ticket.
+  #
+  do_execsql_test 3.0 {
+    DROP TABLE t0;
+    DROP VIEW v2;
+
+    CREATE TABLE t0(c0);
+    INSERT INTO t0(c0) VALUES('');
+    CREATE VIEW v2(c0, c1) AS 
+        SELECT 'B' COLLATE NOCASE, 'a' FROM t0 ORDER BY t0.c0;
+    SELECT SUM(count) FROM (
+      SELECT v2.c1 BETWEEN v2.c0 AND v2.c1 as count FROM v2
+    );
+  } 1
+
+  # The result is 1, as the collation used is the implicit collation sequence
+  # of v2.c1 - BINARY.
+  do_execsql_test 3.1 {
+    SELECT v2.c1 BETWEEN v2.c0 AND v2.c1 as count FROM v2;
+  } 1
+}
+
+finish_test
+