Continue to back away from the LEFT JOIN optimization of check-in [41c27bc0ff1d3135] by disallowing query flattening if the outer query is DISTINCT (#139)

Author: npt-1707

vendor/sqlite3/sqlite3.c

@@ -128093,9 +128093,11 @@ static int flattenSubquery(
   */
   if( (pSubitem->fg.jointype & JT_OUTER)!=0 ){
     isLeftJoin = 1;
-    if( pSubSrc->nSrc>1 || isAgg || IsVirtual(pSubSrc->a[0].pTab) ){
-      /*  (3a)             (3c)     (3b) */
-      return 0;
+    if( pSubSrc->nSrc>1                   /* (3a) */
+     || isAgg                             /* (3b) */
+     || IsVirtual(pSubSrc->a[0].pTab)     /* (3c) */
+     || (p->selFlags & SF_Distinct)!=0    /* (3d) */
+    ){
     }
   }
 #ifdef SQLITE_EXTRA_IFNULLROW