MDEV-28343: sys.create_synonym_db fails with ER_VIEW_SELECT_TMPTABLE when schema contains temporary tables

- MDEV-28342 raised the error in case temporary table shadows base table
- Now we are allowed to shadow base tables with temporary tables and
`sys.create_synonym_db()` can easily check for existance of temporary table and
ignore view creation, since it is not supported to create view from
temporary table.

Reviewed-by: <monty@mariadb.org>,
             <vicentiu@mariadb.org>

mysql-test/suite/sysschema/r/pr_create_synonym_db.result

@@ -61,6 +61,37 @@ create table t (b int);
 create table b(a int);
 create temporary table b (a int);
 call sys.create_synonym_db('db','db_copy');
-ERROR HY000: Table`db`.`b`shadows base table. View cannot be created! Terminating!
+summary
+Created 2 views in the `db_copy` database
+use db_copy;
+show tables;
+Tables_in_db_copy
+a
+t
 drop database db;
 drop database db_copy;
+# MDEV-28343: sys.create_synonym_db fails with ER_VIEW_SELECT_TMPTABLE
+#             when schema contains temporary tables
+#
+create database mytestdb;
+use mytestdb;
+create table t (b int);
+create temporary table tmp (a int);
+call sys.create_synonym_db('mytestdb','db_syn1');
+summary
+Created 1 view in the `db_syn1` database
+use db_syn1;
+show tables;
+Tables_in_db_syn1
+t
+drop database db_syn1;
+use mytestdb;
+create temporary table t (b int);
+call sys.create_synonym_db('mytestdb','db_syn1');
+summary
+Created 0 views in the `db_syn1` database
+use db_syn1;
+show tables;
+Tables_in_db_syn1
+drop database mytestdb;
+drop database db_syn1;

mysql-test/suite/sysschema/t/pr_create_synonym_db.test

@@ -62,8 +62,34 @@ create table a(a int);
 create table t (b int);
 create table b(a int);
 create temporary table b (a int);
---error ER_SIGNAL_EXCEPTION
 call sys.create_synonym_db('db','db_copy');
 
+use db_copy;
+show tables;
+
 drop database db;
 drop database db_copy;
+--echo # MDEV-28343: sys.create_synonym_db fails with ER_VIEW_SELECT_TMPTABLE
+--echo #             when schema contains temporary tables
+--echo #
+
+create database mytestdb;
+use mytestdb;
+create table t (b int);
+# This temporary table will not be created as an view in synonym db
+create temporary table tmp (a int);
+call sys.create_synonym_db('mytestdb','db_syn1');
+use db_syn1;
+show tables;
+drop database db_syn1;
+
+use mytestdb;
+# This temporary table will shadow the base table and no views will be created
+create temporary table t (b int);
+call sys.create_synonym_db('mytestdb','db_syn1');
+
+use db_syn1;
+show tables;
+
+drop database mytestdb;
+drop database db_syn1;

scripts/sys_schema/procedures/create_synonym_db.sql

@@ -98,7 +98,9 @@ BEGIN
     DECLARE v_table VARCHAR(64);
     DECLARE v_views_created INT DEFAULT 0;
     DECLARE v_table_exists ENUM('', 'BASE TABLE', 'VIEW', 'TEMPORARY') DEFAULT '';
-    DECLARE v_temp_table TEXT;
+
+    DECLARE db_doesnt_exist CONDITION FOR SQLSTATE '42000';
+    DECLARE db_name_exists CONDITION FOR SQLSTATE 'HY000';
 
     DECLARE c_table_names CURSOR FOR 
         SELECT TABLE_NAME 
@@ -142,22 +144,9 @@ BEGIN
         IF v_done THEN
             LEAVE c_table_names;
         END IF;
-
+    -- Check the table type, don't support temporary since cannot create the view
-    -- Check does temporary table shadows the base table. If it is so, terminate.
         CALL sys.table_exists(in_db_name, v_table, v_table_exists);
-        IF (v_table_exists = 'TEMPORARY') THEN
+        IF (v_table_exists <> 'TEMPORARY') THEN
-            SET v_temp_table =
-            CONCAT(
-                'Table',
-                 sys.quote_identifier(in_db_name),
-                 '.',
-                 sys.quote_identifier(v_table),
-                 'shadows base table. View cannot be created! Terminating!');
-             SIGNAL SQLSTATE 'HY000'
-                 SET MESSAGE_TEXT = v_temp_table;
-             LEAVE c_table_names;
-        END IF;
-
             SET @create_view_stmt = CONCAT(
                 'CREATE SQL SECURITY INVOKER VIEW ',
                 sys.quote_identifier(in_synonym),
@@ -173,6 +162,7 @@ BEGIN
             DEALLOCATE PREPARE create_view_stmt;
 
             SET v_views_created = v_views_created + 1;
+        END IF;
     END LOOP;
     CLOSE c_table_names;