User defined function - mysql

Question

For some reason, I'm having a lot of troubles with this.
Here is the question:
Write a user-defined sql function named LastNameFirst that concatenates the employee’s LastName and FirstName into a single value named FullName, and displays, in order, the LastName, a comma, a space, and the FirstName (hint: Smith and Steve would be combined to read Smith, Steve). There are many ways to do this without writing a user defined function, but the purpose of this exercise is to write a solution that uses an sql user-defined function.
Here is what I have:
CREATE FUNCTION LastNameFirst
(LastName varchar(50), FirstName varchar(50))
returns varchar(110)
begin
declare Fullname varchar(110);
select CONCAT(LastName, ', ', FirstName)
from prob5
return Fullname;
I'm getting errors all over this thing.. and I don't understand why. Any help would be greatly appreciated.

Answer 1

Irrespective of whether you want a function or a procedure the normal syntax rules for mysql apply - always terminate a statement with ; every begin must have an end etc. A function would look like this
drop function if exists lastnamefirst;
delimiter $$
CREATE FUNCTION LastNameFirst (LastName varchar(50), FirstName varchar(50)) returns varchar(110)
begin
declare Fullname varchar(110);
set fullname = CONCAT(LastName, ', ', FirstName) ;
return Fullname;
end $$
delimiter ;
Note if you are doing this purely in mysql your need to set the delimiter before you create and reset it after.
So given
+----+----------+-----------+
| id | username | photo |
+----+----------+-----------+
| 1 | John | john.png |
| 2 | Jane | jane.png |
| 3 | Ali | |
| 6 | Bruce | bruce.png |
| 7 | Martha | |
+----+----------+-----------+
5 rows in set (0.00 sec)
The function would be invoked like this
select id,username, lastnamefirst(username,ifnull(photo,''))
from users limit 5;
and the result looks like this
+----+----------+------------------------------------------+
| id | username | lastnamefirst(username,ifnull(photo,'')) |
+----+----------+------------------------------------------+
| 1 | John | John, john.png |
| 2 | Jane | Jane, jane.png |
| 3 | Ali | Ali, |
| 6 | Bruce | Bruce, bruce.png |
| 7 | Martha | Martha, |
+----+----------+------------------------------------------+
5 rows in set (0.03 sec)
Beware of nulls in your data and code for them.

Answer 2

Change your function to this -
CREATE FUNCTION LastNameFirst (LastName varchar(50), FirstName varchar(50)) returns varchar(110)
return concat(LastName, ", ", FirstName);
And then you can use it like this -
select LastNameFirst(LastName, FirstName) from prob5;