How to determine the length of a sql function input

Question

How can I make sure my function only works with inputs with a certain length?

for example:

I want my function to work with ID´s that have at least the length 3 but not more than 8?

Answer 1

As explained in this SO answer, you can define your own function that returns error message and call it from the validation function to return an error, e.g.:

CREATE FUNCTION F_PROCESS(ID VARCHAR(8)) RETURNS VARCHAR
BEGIN

  DECLARE RETURN_VAR VARCHAR DEFAULT "";

  IF(LENGTH(ID) < 3) THEN
    CALL raise_error('ID must have at least 3 characters')
  END IF;
  RETURN RETURN_VAR;
END;//

Here, LENGTH function checks for the lower bound whereas declaration checks for the upper bound.