A function that takes a parameter, performs an operation using an SQL function, and returns the result : Function « Procedure Function « MySQL Tutorial

1. MySQL Tutorial
2. Procedure Function
3. Function

In this case, it is unnecessary to use delimiter because the function definition contains no internal ; statement delimiters:

mysql>
mysql>
mysql> CREATE FUNCTION hello (s CHAR(20)) RETURNS CHAR(50)
    ->     RETURN CONCAT('Hello, ',s,'!');
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql>
mysql> SELECT hello('world');
+----------------+
| hello('world') |
+----------------+
| Hello, world!  |
+----------------+
1 row in set (0.00 sec)

mysql>
mysql>
mysql> drop function hello;
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql>