Changed handling of mergeable views/derived tables of one table.

mysql-test/main/func_dep.result

@@ -4395,13 +4395,16 @@ FROM t1 LEFT JOIN (
 SELECT t2.c,COALESCE(t2.c,2) as x FROM t2) AS d
 ON 1
 GROUP BY d.c;
-ERROR 42000: Non-grouping field 'x' is used in SELECT list
+c	x
+NULL	2
+2	2
 SELECT d.c,d.x
 FROM t1 LEFT JOIN (
 SELECT t2.c,COALESCE(t2.c,2) as x FROM t2) AS d
 ON 0
 GROUP BY d.c;
-ERROR 42000: Non-grouping field 'x' is used in SELECT list
+c	x
+NULL	NULL
 SELECT t1.a,d.c,d.x
 FROM t1 LEFT JOIN (
 SELECT t2.c,COALESCE(t2.c,2) as x FROM t2) AS d

mysql-test/main/func_dep.test

@@ -3924,14 +3924,12 @@ FROM t1 LEFT JOIN (
 ON (t1.a > 0)
 GROUP BY d.c;
 
---error ER_NON_GROUPING_FIELD_USED
 SELECT d.c,d.x
 FROM t1 LEFT JOIN (
   SELECT t2.c,COALESCE(t2.c,2) as x FROM t2) AS d
 ON 1
 GROUP BY d.c;
 
---error ER_NON_GROUPING_FIELD_USED
 SELECT d.c,d.x
 FROM t1 LEFT JOIN (
   SELECT t2.c,COALESCE(t2.c,2) as x FROM t2) AS d

sql/sql_func_dep.cc

@@ -825,7 +825,9 @@ bool expand_fdfs_with_join_tables_fields(FD_select_info *sl_info,
     TABLE_LIST *tbl= dep_tabs.elem(i);
     if (!tbl->on_expr)
       continue;
-    if (tbl->nested_join && expand_fdfs_with_join_tables_fields(sl_info, tbl))
+    if (tbl->nested_join &&
+        (tbl->nested_join->join_list.elements > 1) &&
+        expand_fdfs_with_join_tables_fields(sl_info, tbl))
       return true;
     else if (tbl->table)
     {
@@ -902,7 +904,7 @@ bool expand_fdfs_with_top_join_tables_fields(FD_select_info *sl_info)
     TABLE_LIST *tbl= dep_tabs.elem(i);
     if (!tbl->on_expr)
       continue;
-    if (tbl->nested_join)
+    if (tbl->nested_join && (tbl->nested_join->join_list.elements > 1))
     {
       if (tbl->outer_join & JOIN_TYPE_LEFT)
         sl_info->top_level= false;