What is in a index?

Answer 1

An index is a performance-tuning method of allowing faster retrieval of records. An index creates an entry for each value that appears in the indexed columns. By default, Oracle creates B-tree indexes

The syntax for creating a index is:

CREATE [UNIQUE] INDEX index_name

ON table_name (column1, column2, . column_n)

[ COMPUTE STATISTICS ];

UNIQUE indicates that the combination of values in the indexed columns must be unique.

COMPUTE STATISTICS tells Oracle to collect statistics during the creation of the index. The statistics are then used by the optimizer to choose a "plan of execution" when SQL statements are executed.