Basic Oracle Concepts and Programming Question:

Answer #1If 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';
<pre>INDEX_NAME TABLE_NAME UNIQUENES
----------------------- --------------------- ---------
SYS_C004123 STUDENT UNIQUE
SYS_C004124 STUDENT UNIQUE
STUDENT_NAMES STUDENT NONUNIQUE</pre>

Answer #2SELECT index_name, table_name, column_name
FROM USER_IND_COLUMNS WHERE table_name = 'STUDENT';
<pre>INDEX_NAME TABLE_NAME COLUMN_NAME
-------------------- ---------------- ----------------
SYS_C004135 STUDENT ID
SYS_C004136 STUDENT SOCIAL_NUMBER
STUDENT_NAMES STUDENT FIRST_NAME
STUDENT_NAMES STUDENT LAST_NAME </pre>
The USER_IND_COLUMNS view confirms that index STUDEND_NAMES has two columns FIRST_NAME and LAST_NAME.