If you know a group of multiple columns will be always used together as search criteria, you should create a single index for that group of columns with the "ON table_name(col1, col2, ...)" clause. Here is an example of one index for two columns:

CREATE TABLE student (id NUMBER(5) PRIMARY KEY,

first_name VARCHAR(80) NOT NULL,

last_name VARCHAR(80) NOT NULL,

birth_date DATE NOT NULL,

social_number VARCHAR(80) UNIQUE NOT NULL);

Table created.

CREATE INDEX student_names ON student(first_name,last_name);

Index created.

SELECT index_name, table_name, uniqueness

FROM USER_INDEXES WHERE table_name = 'STUDENT';

INDEX_NAME   TABLE_NAME  UNIQUENES

----------------------- --------------------- ---------

SYS_C004123   STUDENT   UNIQUE

SYS_C004124   STUDENT   UNIQUE

STUDENT_NAMES   STUDENT   NONUNIQUE