Indexes in SQL

Indexing is a database technique used to speed up data retrieval. It allows the database management system to quickly locate specific data without scanning every row in a table.

Key Points about Indexing

• Analogy: Indexing can be compared to an index in a textbook, which helps readers quickly find topics without reading the entire book.
• Data Structure: Indexes are typically stored in a B-tree structure, which allows for faster searches with logarithmic time complexity (O(log N)).
• Importance:
  • Faster Queries: Reduces the time taken to find specific data by enabling quick lookups.
  • Efficiency: Particularly beneficial in large databases, where searching through every row would be inefficient.
  • Automatic Indexing: Primary keys are automatically indexed when created, simplifying data management.

Creating an Index

The basic syntax for creating an index in SQL is:

CREATE INDEX index_name ON table_name (column_name);

Handling Transactions and Rollbacks

Transactions in databases are essential for maintaining data integrity and ensuring that operations involving multiple steps are completed reliably. A transaction can be defined as a sequence of operations that are treated as a single unit of work.

In SQL, a transaction is a sequence of operations performed as a single logical unit of work. A transaction follows four key properties, often referred to as ACID:

1. Atomicity: All operations in a transaction are treated as a single unit. If any part fails, the entire transaction fails.
2. Consistency: A transaction must bring the database from one valid state to another valid state.
3. Isolation: Transactions are isolated from each other. Concurrent transactions should not interfere with each other.
4. Durability: Once a transaction is committed, its changes are permanent, even in the event of a system failure.

How to Handle Transactions in SQL

Let’s look at how we can use transactions in SQL. In PostgreSQL, we can manage transactions using the following commands: