MySQL - Storing variables inside CREATE FUNCTION - mysql

Question

I'm trying to figure out how to store variables inside a function in mySQL. I am trying to create a function that capitalizes a field name. Creating a function works if I don't create variables. The problem is this is difficult to read, and is easy to make mistakes with.
CREATE FUNCTION capitalize(string TEXT)
RETURNS TEXT
RETURN CONCAT(UPPER(LEFT(string,1)), LOWER(RIGHT(string, LENGTH(string) - 1)));
When I try to add variables using the DECLARE and SET keywords, it no longer works.
CREATE FUNCTION capitalize(string TEXT)
RETURNS TEXT
DECLARE first_letter TEXT;
DECLARE last_letters TEXT;
SET first_letter = UPPER(LEFT(string,1));
SET last_letters = LOWER(RIGHT(string, LENGTH(string) - 1));
RETURN CONCAT(first_letter, last_letters);
I get this error message
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 4
I've fiddled around with it, removing semicolons, and double/triple checking parentheses. I've fiddled with BEGIN and END statements but nothing seems to work at all.
I have searched extensively on this topic but cannot figure out where the problem lies.

Answer 1

The body of a CREATE FUNCTION can consist of only a single statement, which is why the first version works and the second doesn't. Fortunately, that single statement can be a compound statement enclosed in a BEGIN ... END block.
You need to enclose the function body in a BEGIN ... END block to allow MySQL to see it as a single statement; you'll also perhaps need to precede and follow it with DELIMITER statements (depending on your client, as Mr. Berkowski points out):
DELIMITER //
CREATE FUNCTION capitalize(string TEXT)
RETURNS TEXT
BEGIN
DECLARE first_letter TEXT;
DECLARE last_letters TEXT;
SET first_letter = UPPER(LEFT(string,1));
SET last_letters = LOWER(RIGHT(string, LENGTH(string) - 1));
RETURN CONCAT(first_letter, last_letters);
END; //
DELIMITER ;
(Note especially the space between the last DELIMITER and the semicolon.)