MDEV-16473 WITH statement throws 'no database selected' error

Different fix, just use NULL, not no_db,

mysql-test/r/cte_nonrecursive.result

@@ -1511,15 +1511,4 @@ a	a
 3	3
 1	1
 drop database db_mdev_16473;
-create database `*` ;
-create table `*`.t1 (a int);
-insert into `*`.t1 values (2), (7), (3), (1);
-use `*`;
-select * from t1;
-a
-2
-7
-3
-1
-drop database `*`;
 use test;

mysql-test/t/cte_nonrecursive.test

@@ -1056,11 +1056,4 @@ select * from cte, db_mdev_16473.t1 as t where cte.a=t.a;
 
 drop database db_mdev_16473;
 
-create database `*` ;
-create table `*`.t1 (a int);
-insert into `*`.t1 values (2), (7), (3), (1);
-use `*`;
-select * from t1;
-drop database `*`;
-
 use test;

sql/sql_acl.cc

@@ -7581,7 +7581,7 @@ bool check_grant(THD *thd, ulong want_access, TABLE_LIST *tables,
       tl->correspondent_table ? tl->correspondent_table : tl;
     sctx= t_ref->security_ctx ? t_ref->security_ctx : thd->security_ctx;
 
-    if (tl->with ||
+    if (tl->with || !tl->db ||
         (tl->select_lex &&
          (tl->with= tl->select_lex->find_table_def_in_with_clauses(tl))))
       continue;

sql/sql_base.cc

@@ -1531,6 +1531,12 @@ bool open_table(THD *thd, TABLE_LIST *table_list, Open_table_context *ot_ctx)
     DBUG_RETURN(true);
   }
 
+  if (!table_list->db)
+  {
+    my_error(ER_NO_DB_ERROR, MYF(0));
+    DBUG_RETURN(true);
+  }
+
   key_length= get_table_def_key(table_list, &key);
 
   /*
@@ -3330,14 +3336,6 @@ open_and_process_table(THD *thd, LEX *lex, TABLE_LIST *tables,
   /*
     Not a placeholder: must be a base/temporary table or a view. Let us open it.
   */
-
-  if (tables->no_default_db && !tables->is_fqtn)
-  {
-    my_message(ER_NO_DB_ERROR, ER(ER_NO_DB_ERROR), MYF(0));
-    error= TRUE;
-    goto end;
-  }
-
   if (tables->table)
   {
     /*

sql/sql_class.h

@@ -3959,12 +3959,9 @@ public:
         my_message(ER_NO_DB_ERROR, ER(ER_NO_DB_ERROR), MYF(0));
         return TRUE;
       }
-      /*
-        It does not matter what database name is set in this case
-        because it will never be used after parser stage
-      */
-      *p_db_length= strlen(no_db);
-      *p_db= strmake(no_db, *p_db_length);
+      /* This will allow to throw an error later for non-CTE references */
+      *p_db= NULL;
+      *p_db_length= 0;
     }
     else
     {

sql/sql_lex.h

@@ -156,8 +156,6 @@ struct LEX_TYPE
 extern const LEX_STRING null_lex_str;
 extern const LEX_STRING empty_lex_str;
 
-extern const char *no_db;
-
 enum enum_sp_suid_behaviour
 {
   SP_IS_DEFAULT_SUID= 0,

sql/sql_parse.cc

@@ -139,7 +139,6 @@ static bool execute_show_status(THD *, TABLE_LIST *);
 static bool check_rename_table(THD *, TABLE_LIST *, TABLE_LIST *);
 
 const char *any_db="*any*";	// Special symbol for check_access
-const char *no_db="*";          // Used when no default db is set
 
 const LEX_STRING command_name[257]={
   { C_STRING_WITH_LEN("Sleep") },           //0
@@ -6685,11 +6684,7 @@ check_access(THD *thd, ulong want_access, const char *db, ulong *save_priv,
   THD_STAGE_INFO(thd, stage_checking_permissions);
   if ((!db || !db[0]) && !thd->db && !dont_check_global_grants)
   {
-    DBUG_PRINT("error",("No database"));
-    if (!no_errors)
-      my_message(ER_NO_DB_ERROR, ER_THD(thd, ER_NO_DB_ERROR),
-                 MYF(0));                       /* purecov: tested */
-    DBUG_RETURN(TRUE);				/* purecov: tested */
+    DBUG_RETURN(FALSE); // CTE reference or an error later
   }
 
   if ((db != NULL) && (db != any_db))
@@ -8188,7 +8183,6 @@ TABLE_LIST *st_select_lex::add_table_to_list(THD *thd,
     DBUG_RETURN(0);
   else
     ptr->is_fqtn= FALSE;
-  ptr->no_default_db= !thd->db && !(lex->sphead && lex->sphead->m_name.str);
 
   ptr->alias= alias_str;
   ptr->is_alias= alias ? TRUE : FALSE;
@@ -8301,7 +8295,7 @@ TABLE_LIST *st_select_lex::add_table_to_list(THD *thd,
   lex->add_to_query_tables(ptr);
 
   // Pure table aliases do not need to be locked:
-  if (!MY_TEST(table_options & TL_OPTION_ALIAS))
+  if (ptr->db && !(table_options & TL_OPTION_ALIAS))
   {
     ptr->mdl_request.init(MDL_key::TABLE, ptr->db, ptr->table_name, mdl_type,
                           MDL_TRANSACTION);

sql/table.h

@@ -2095,8 +2095,7 @@ struct TABLE_LIST
       qualified name (<db_name>.<table_name>).
   */
   bool          is_fqtn;
-  /** TRUE if no default database is defined for the table name */
-  bool          no_default_db;
+
   /* TRUE <=> derived table should be filled right after optimization. */
   bool          fill_me;
   /* TRUE <=> view/DT is merged. */