B-tree index – Oracle PL/SQL Tutorial

A B-tree index in Oracle’s PL/SQL is a data structure that allows for efficient retrieval of data in a database table. The term “B-tree” stands for balanced tree, and it’s a type of self-balancing search tree data structure. B-tree indexes are commonly used in database management systems to speed up the retrieval of data by providing a quick and efficient way to locate specific rows within a table.

Here are some key points about Oracle PL/SQL B-tree indexes:

Structure:

A B-tree index is organized as a tree structure with a root node, intermediate nodes, and leaf nodes.
The tree is balanced, meaning that the depth of the tree is kept relatively constant, ensuring efficient search operations.

Balancing:

As data is inserted or deleted, the B-tree structure automatically balances itself to maintain optimal search performance.
This self-balancing property ensures that the tree remains relatively shallow, and the number of comparisons needed to find a specific value is minimized.

Search Efficiency:

B-tree indexes provide efficient search operations. The time complexity for search operations is logarithmic, making them well-suited for large datasets.
The balanced structure ensures that the search path from the root to a leaf node is relatively short.

Index Key:

In PL/SQL, B-tree indexes are created based on one or more columns of a table.
The indexed columns are organized in the B-tree, allowing for quick access to rows based on the values of those columns.

Unique and Non-Unique Indexes:

B-tree indexes can be unique or non-unique.
Unique indexes ensure that the indexed columns have unique values, while non-unique indexes allow duplicate values.

Creating B-tree Indexes:

In Oracle PL/SQL, you can create a B-tree index using the CREATE INDEX statement.

Example:

CREATE INDEX student_idx
ON STUDENTS_LIST (student_id);

Performance Impact:

B-tree indexes improve the performance of queries that involve conditions in the WHERE clause related to the indexed columns.
However, they may introduce some overhead during data modification operations (inserts, updates, and deletes) as the index needs to be maintained.

Check index:

select INDEX_NAME, INDEX_TYPE, TABLE_NAME
from USER_INDEXES
WHERE table_name='STUDENTS_LIST';

Output:

INDEX_NAME	INDEX_TYPE	TABLE_NAME
STUDENT_IDX	NORMAL	STUDENTS_LIST

Dropping Indexes:

You can drop a B-tree index using the DROP INDEX statement.

DROP INDEX student_idx;

In summary, Oracle PL/SQL B-tree indexes play a crucial role in optimizing query performance by providing a balanced and efficient data structure for quick data retrieval. They are a fundamental component of database design and management, especially in scenarios where quick access to specific rows based on certain criteria is essential.

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