MariaDB [test]> create table t1 ( id int primary key auto_increment, name varchar(10));
Query OK, 0 rows affected (0.011 sec)

MariaDB [test]> insert into t1 (name) values ('wrbyviwb');
Query OK, 1 row affected (0.004 sec)

MariaDB [test]> insert into t1 (name) values ('wrbyrwb1');
Query OK, 1 row affected (0.003 sec)

MariaDB [test]> insert into t1 (name) values ('wrbrwb3');
Query OK, 1 row affected (0.003 sec)

MariaDB [test]> DELIMITER //
MariaDB [test]> DROP FUNCTION IF EXISTS t1test//
Query OK, 0 rows affected, 1 warning (0.002 sec)

MariaDB [test]> CREATE FUNCTION t1test(val INT) RETURNS varchar(400) CHARSET utf8
    -> BEGIN
    -> DECLARE output VARCHAR(400) DEFAULT '';
    -> 
    -> 
    -> SET output = (select cnt.name from t1 cnt join ( select CNT.id from t1 CNT where CNT.id=val) t2 on t2.id=cnt.id);
    -> RETURN output;
    -> END//
Query OK, 0 rows affected (0.006 sec)

MariaDB [test]> DELIMITER ;
MariaDB [test]> 
MariaDB [test]> select t1test(1);
ERROR 1146 (42S02): Table 'test.CNT' doesn't exist
MariaDB [test]> 
MariaDB [test]> DELIMITER //
MariaDB [test]> DROP FUNCTION IF EXISTS t1test//
Query OK, 0 rows affected (0.006 sec)

MariaDB [test]> CREATE FUNCTION t1test(val INT) RETURNS varchar(400) CHARSET utf8
    -> BEGIN
    -> DECLARE output VARCHAR(400) DEFAULT '';
    -> DECLARE output1 VARCHAR(400) DEFAULT '';
    -> DECLARE output2 VARCHAR(400) DEFAULT '';
    -> 
    -> SET output1 = (select Cnt.name from t1 Cnt where Cnt.id=val);
    -> SET output = (select cnt.name from t1 cnt where cnt.id=val);
    -> SET output2 = (select cnt.name from t1 cnt join ( select cnt.id from t1 cnt where cnt.id=val) sub1 on sub1.id=cnt.id);
    -> RETURN output2;
    -> END//
Query OK, 0 rows affected (0.006 sec)

MariaDB [test]> DELIMITER ;
MariaDB [test]> 
MariaDB [test]> 
MariaDB [test]> select t1test(1);
ERROR 1146 (42S02): Table 'test.cnt' doesn't exist
MariaDB [test]> 
MariaDB [test]> 
MariaDB [test]> select @@version
    -> ;
+---------------------+
| @@version           |
+---------------------+
| 10.6.21-MariaDB-log |
+---------------------+
1 row in set (0.000 sec)

MariaDB [test]>