Function for checking list similarities on PostgreSQL

CREATE_FUNCTION_GET_LIST_SIMILARITY.sql

CREATE OR REPLACE FUNCTION SF_GET_LIST_SIMILARITY(
    p_list1 text[],
    p_list2 text[]
) RETURNS NUMERIC(19,4) AS $$
DECLARE
    w_list text[] := '{}';
BEGIN
    IF p_list1 IS NULL OR p_list2 IS NULL THEN
        RETURN 0;
    END IF; 

    IF array_length(p_list1, 1) = 0 OR array_length(p_list2, 1) = 0 THEN
        RETURN 0;
    END IF; 

    FOR i IN 1..array_length(p_list1, 1) LOOP
        IF p_list1[i] = ANY(p_list2) THEN
            w_list := array_append(w_list, p_list1[i]);
        END IF; 
    END LOOP;

    RETURN array_length(w_list, 1)::numeric(19,4) / array_length(p_list1, 1)::numeric(19,4);
END;
$$ LANGUAGE plpgsql;