Undeclared variable compid in mariaddb function

Question

i try to create function to get id of company by phone number(varchar)

CREATE OR REPLACE FUNCTION getIdByPhone (cp CHAR(255))
RETURNS  INT
BEGIN 
SELECT id into compid 
FROM companies 
WHERE comp_phone1=cp;
RETURN compid;
END;

and have error:

Undeclared variable: compid

Answer 1

The error message is trying to tell you. You need to declare the variable before you can assign to it:

delimiter //

create function getidbyphone (cp char(255))
returns int
deterministic
begin 
    declare compid int;
    select id into compid from companies where comp_phone1 = cp;
    return compid;
end
//

delimiter;

Here is a Demo on DB Fiddle.