Help with "Expression as an assignment target" error

simple question here, I am writing a function, but I was having trouble setting up my first if statement, my attempt is below, but I keep getting "Expression can not be used as an assignment target" error on the lines "Type := CE;" and "Type :=UG;" Im sure there is a quick fix to this.开发者_运维百科..... anyone know?

CREATE OR REPLACE FUNCTION SCHEMA1."FUNCTION1" (   Id   IN VARCHAR2,
                                                   term IN VARCHAR2,
                                                   Type IN VARCHAR2 default NULL )
RETURN VARCHAR2 IS


BEGIN
IF Type IS NULL
THEN
    IF SUBSTR(term,5,6) = 'Q'
    THEN
        Type := 'CE';
    ELSE
        Type := 'UG';
    END IF;
END IF;
........

Declare a holding variable for use within the function?

CREATE OR REPLACE FUNCTION SCHEMA1."FUNCTION1" (   Id   IN VARCHAR2,
                                                   term IN VARCHAR2,
                                                   Type IN VARCHAR2 default NULL )
RETURN
  VARCHAR2
IS
  iType VARCHAR2;    
BEGIN

iType := Type;

IF iType IS NULL
THEN
    IF SUBSTR(term,5,6) = 'Q'
    THEN
        iType := 'CE';
    ELSE
        iType := 'UG';
    END IF;
END IF;
........

Looks to me like you're passing 'Type' in as an argument and then trying to assign to it. Is your intent to RETURN 'CE'/'UG' based on Term? If so, introduce a new variable or change Type := to RETURN.