Introduction: Why Indexes Matter in Oracle SQL

      Indexes are a crucial aspect of Oracle SQL, significantly improving the performance of database queries by enabling fast access to data. In this guide, we’ll explore the different types of indexes in Oracle SQL, how they work, and their benefits. By the end of this post, you’ll have a solid understanding of indexes and how to use them to optimize your SQL queries. You can learn more about Oracle’s indexing technology by reading the official documentation.

What Are Indexes in Oracle SQL?

Indexes in Oracle SQL are specialized database objects designed to enhance the performance of query operations. They allow for faster data retrieval by reducing the need for full table scans. Oracle can use an index to locate the exact rows needed to satisfy a query’s criteria, greatly improving query execution speed.

Types of Indexes in Oracle SQL

Oracle SQL offers a variety of index types, each designed for specific use cases. Let’s take a closer look at the most commonly used index types.

1. B-Tree Indexes: The Default Choice for Most Queries

B-Tree (Balanced Tree) indexes are the most commonly used index type in Oracle SQL. They are suitable for columns with a high cardinality (lots of unique values) and provide an ordered list of values divided into ranges. Thus, they can significantly speed up searches for high-cardinality columns.

• Example:

1. 1. Account number in a banking system
   2. Student registration number
   3. Employee ID

• How to Create and Manage B-Tree Indexes
• • Create Index:
    • Use this SQL statement to create an index. You need to specify the table and column(s) on which the index is created and choose the index type. Use below SQL command to create an index .

    • Syntax:
      CREATE INDEX index_name on table_name(column_name);
      
      Example:
      CREATE INDEX idx_btree_emp on emp(emp_no);

• • Drop Index:
    • To remove an index, you can use the DROP INDEX statement. This operation should be performed with caution, as it can impact query performance. Use below SQL command to drop an existing index.

    • Syntax:
      DROP INDEX index_name;
      
      Example:
      DROP INDEX idx_btree_emp;

• • Alter Index:
    • The ALTER INDEX statement allows you to modify an existing index, such as changing its storage options or rebuilding it for performance reasons.

    • Syntax:
      ALTER INDEX current_index_name
      RENAME TO new_indexname;
      
      Example:
      ALTER INDEX btree_ind_emp
      RENAME TO btree_ind_emp_new;

2. Bitmap Indexes: Ideal for Low Cardinality Data

Bitmap indexes are particularly effective for columns with a low number of distinct values. Therefore, they are often used in data warehousing applications, where low-cardinality columns are common.

• Example:
  1. Movie ratings(1-10)
  2. Color Categories(Red, Blue, Green, Yellow etc.)
• How to Create and Manage Bitmap Indexes
  
  • Create Bitmap Index:
    
    • Use this SQL statement to create an index. You need to specify the table and column(s) on which the index is created and choose the index type. Use below SQL command to create an index .

    • Syntax:
      CREATE BITMAP INDEX index_name ON table_name(column_name);
      
      Example:
      CREATE BITMAP INDEX idx_bitmap_dept_no ON t_dept_det(dept_no);

  • Drop Index:
    • To remove an index, you can use the DROP INDEX statement. This operation should be performed with caution, as it can impact query performance. Use below SQL command to drop an existing index.

    • Syntax:
      DROP INDEX index_name;
      
      Example:
      DROP INDEX idx_btree_emp;

  • Alter Index:
    • The ALTER INDEX statement allows you to modify an existing index, such as changing its storage options or rebuilding it for performance reasons.

    • Syntax:
      ALTER INDEX current_index_name
      RENAME TO new_indexname;
      
      Example:
      ALTER INDEX idx_bitmap_dept_no
      RENAME TO idx_bitmap_dept_number ;

3. Function-Based Indexes: Indexing Expressions or Calculations

Function-based indexes are helpful when you need to optimize queries that involve expressions or calculations. For example, you can create an index on the result of a function applied to a column.

• Example:

1. 1. Creating an index on the uppercase version of a name field.

• How to Create and Manage Function-Based Indexes
  
  • Create Function-Based Index:
    

    • Syntax:
      CREATE INDEX idx_name ON table_name(function(column_name));
      
      Example:
      CREATE INDEX idx_fun_emp_name ON emp(UPPER(emp_name));

  • Drop Function-Based Index:
    

    • Syntax:
      DROP INDEX index_name;
      
      Example:
      DROP INDEX idx_fun_emp_name ;

  • Alter Function-Based Index:
    

    • Syntax:
      ALTER INDEX current_index_name
      RENAME TO new_indexname;
      
      Example:
      ALTER INDEX idx_fun_emp_name
      RENAME TO idx_fun_upper_emp_name ;

4. Reverse Key Indexes: Preventing Index Block Contention

Reverse key indexes are a special type of B-Tree index where the bytes of the index key are reversed before storage. As a result, this type of index is useful to prevent index block contention when many rows are inserted concurrently.

• How to Create and Manage Reverse Key Indexes
  
  • Create Reverse Key Index:
    

    • Syntax:
      CREATE INDEX index_name on table_name(column_name) REVERSE;
      
      Example:
      CREATE INDEX idx_btree_emp on emp(sal) REVERSE;

  • Drop Reverse Key Index:
    

    • Syntax:
      DROP INDEX index_name;
      
      Example:
      DROP INDEX idx_btree_emp;

  • Alter Reverse Key Index:
    

    • Syntax:
      ALTER INDEX current_index_name
      RENAME TO new_indexname;
      
      Example:
      ALTER INDEX idx_btree_emp
      RENAME TO idx_btree_emp_new;

5. Composite Indexes: Indexing Multiple Columns

A composite index is an index created on multiple columns. Therefore, it is especially beneficial for queries that filter on one or more of the indexed columns.

• How to Create and Manage Composite Indexes
• • Create Composite Index:
    

    • Syntax:
      CREATE INDEX index_name on table_name(multiple_column_name);
      
      Example:
      CREATE INDEX idx_comp_emp ON t_emp_det(sal,dept_id);

  • Drop Composite Index:
    

    • Syntax:
      DROP INDEX index_name;
      
      Example:
      DROP INDEX idx_comp_emp;

  • Alter Composite Index:
    

    • Syntax:
      ALTER INDEX current_index_name
      RENAME TO new_indexname;            
      
      Example:
      ALTER INDEX idx_comp_emp
      RENAME TO idx_comp_emp_sal_deptno;

Best Practices for Using Indexes in Oracle SQL

To maximize the benefits of indexes, consider the following best practices:

• Index Selectively: 
  1. Index only the columns that are frequently used in WHERE clauses or JOIN conditions. Over-indexing can lead to performance degradation, so it’s essential to choose the right columns.

• Avoid Indexing Small Tables:
  1. For very small tables, full table scans may be faster than using indexes. In such cases, it’s better to avoid indexing the table.

• Be Mindful of Table Updates:
  1. Indexes need to be updated when the underlying table data changes. Excessive inserts, updates, or deletes can impact performance, so ensure that your indexes are optimized for your workload.

• Leverage Oracle’s Query Optimizer:
  1. Oracle’s query optimizer can often determine the best execution plan for your queries. Trusting the optimizer is usually more efficient than manually forcing the use of a particular index.

Conclusion: The Power of Indexes in Oracle SQL

Indexes play a critical role in optimizing query performance in Oracle SQL. By understanding the different types of indexes and how to create and manage them, you can significantly improve the speed and efficiency of your SQL queries.

Remember, though, that indexing should be used judiciously to avoid performance issues. When done right, indexes will help ensure your database remains fast and responsive. To learn more about the Oracle views , don’t forget to check our complete guide related to oracle views.

Happy Learning!!!