MDEV-25080 Fix incorrect view names in printed queries

When printing Item_direct_view_ref the printed field name must be
complemented with the view name/derived table alias.
For example, for "SELECT a FROM (SELECT a FROM t1) q" field `a`
in the select list must be printed as `q`.`a`.

But if the view was merged then the initial `q` does not make sense
any more so field `a` must be printed  as `t1`.`a`

mysql-test/main/myisam_explain_non_select_all.result

@@ -2723,7 +2723,7 @@ EXPLAIN EXTENDED DELETE   FROM v1 WHERE a < 4;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	t1	range	PRIMARY	PRIMARY	4	NULL	3	100.00	Using where
 Warnings:
-Note	1003	/* select#1 */ delete  from `test`.`t1` using dual where `test`.`t1`.`a` < 4
+Note	1003	/* select#1 */ delete  from `test`.`t1` using dual where `v1`.`a` < 4
 # Status of EXPLAIN EXTENDED query
 Variable_name	Value
 Handler_read_key	3

mysql-test/main/opt_trace.result

@@ -59,7 +59,7 @@ select * from v1	{
             }
           },
           {
-            "expanded_query": "/* select#1 */ select t1.a AS a,t1.b AS b from v1"
+            "expanded_query": "/* select#1 */ select v1.a AS a,v1.b AS b from v1"
           }
         ]
       }
@@ -230,7 +230,7 @@ select * from (select * from t1 where t1.a=1)q	{
             }
           },
           {
-            "expanded_query": "/* select#1 */ select t1.a AS a,t1.b AS b from (/* select#2 */ select t1.a AS a,t1.b AS b from t1 where t1.a = 1) q"
+            "expanded_query": "/* select#1 */ select q.a AS a,q.b AS b from (/* select#2 */ select t1.a AS a,t1.b AS b from t1 where t1.a = 1) q"
           }
         ]
       }
@@ -695,7 +695,7 @@ explain select * from v2	{
             }
           },
           {
-            "expanded_query": "/* select#1 */ select t2.a AS a from v2"
+            "expanded_query": "/* select#1 */ select v2.a AS a from v2"
           }
         ]
       }

mysql-test/main/opt_trace_security.result

@@ -197,7 +197,7 @@ select * from db1.v1	{
             }
           },
           {
-            "expanded_query": "/* select#1 */ select db1.t1.a AS a from v1"
+            "expanded_query": "/* select#1 */ select v1.a AS a from v1"
           }
         ]
       }

mysql-test/suite/federated/federatedx_create_handlers.test

@@ -381,6 +381,7 @@ connection slave;
 DROP TABLES federated.t1, federated.t2, federated.t3, federated.t10,
    federated.t11;
 
+
 --echo # MDEV-25080: Allow pushdown of queries involving UNIONs
 --echo #   in outer select to foreign engines
 --echo #

sql/item.cc

@@ -10866,6 +10866,25 @@ table_map Item_direct_view_ref::not_null_tables() const
    return get_null_ref_table()->map;
 }
 
+void Item_direct_view_ref::print(String *str, enum_query_type query_type)
+{
+  /*
+    If the view/derived table was not merged then this field name must
+    be complemented with the view name/derived table alias.
+    For example, for "SELECT a FROM (SELECT a FROM t1) q" field `a` in the
+    select list must be printed as `q`.`a`.
+    Ancestor class Item_ident contains the correct table_name for that case.
+    But if the view was merged then the initial `q` does not make sense
+    any more so print the Item_ref contents. Field `a` will be printed
+    as `t1`.`a` then
+  */
+  if (!view->merged)
+    Item_ident::print(str, query_type);
+  else
+    Item_ref::print(str, query_type);
+
+}
+
 /*
   we add RAND_TABLE_BIT to prevent moving this item from HAVING to WHERE
 */

sql/item.h

@@ -6238,6 +6238,7 @@ public:
   Item *field_transformer_for_having_pushdown(THD *, uchar *) override
   { return this; }
   Item *remove_item_direct_ref() override { return this; }
+  void print(String *str, enum_query_type query_type) override;
 };