SQL & PL/SQL

Given the table (simple, made-up example):

CREATE TABLE applicant_diversity_info (
applicant_diversity_id NUMBER(12), PRIMARY KEY(applicant_diversity_id),
apply_date DATE,
ssn_salted_md5 RAW(16),
gender CHAR(1), CHECK ( (gender IS NULL OR gender IN ('M','F')) ),
racial_continent VARCHAR2(30), CHECK ( (racial_continent IS NULL
OR racial_continent IN ('Europe','Africa','America','Asia_Pacific')) ),
ethnic_supergroup VARCHAR2(30), CHECK ( (ethnic_supergroup IS NULL OR ethnic_supergroup IN ('Latin American','Other')) ),
hire_salary NUMBER(11,2),
hire_month DATE,
termination_salary NUMBER(11,2),
termination_month DATE,
termination_cause VARCHAR2(30), CHECK ( (termination_cause IS NULL
OR termination_cause IN ('Resigned','Leave of Absence','Laid Off','Performance','Cause')) )
);

Oracle (syntactically) allows me to create either one BITMAP index over all four small-cardinality columns

CREATE BITMAP INDEX applicant_diversity_diversity_idx ON applicant_diversity_info (
gender, racial_continent, ethnic_supergroup, termination_reason );

or four independent indexes

CREATE BITMAP INDEX applicant_diversity_gender_idx ON applicant_diversity_info ( gender );
CREATE BITMAP INDEX applicant_diversity_race_idx ON applicant_diversity_info ( raceial_continent );
etc.

What is the difference between the two approaches; is there any meaningful difference in disk-space between the one multi-colum index and the four single-column indexes? Does it make a difference in what the query-planner will consider?

And, if I define one multi-column BITMAP index, does the order of columns matter?