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Indexing for Performance

Introduction​

SQL is a powerful language used to interact with relational databases. One of the most critical aspects of working with SQL databases is performance tuning. In this tutorial, we will focus on a key strategy for improving the performance of SQL queries: Indexing.

What is Indexing?​

An index in SQL is a data structure that improves the speed of data retrieval operations on a database table. It's similar to the index in a book. Without an index, the SQL server reads through all rows, known as a table scan, to retrieve the desired data. However, with an index, it goes directly to the location where the data is stored, which significantly speeds up the data retrieval process.

Types of Indexes​

There are several types of indexes in SQL:

  1. Clustered Index: There can only be one clustered index per table, which rearranges the way records in the table are physically stored. Therefore, it sorts and stores the data rows in the table based on their key values.

  2. Non-clustered Index: A non-clustered index doesn't alter the way the records are stored in the table but creates a separate object within the table that points back to the original table rows after it sorts them. A table can have multiple non-clustered indexes.

  3. Unique Index: This ensures the data across all the rows in the index key columns is unique. It is used to prevent duplicate entries in the column or combination of columns where the index is implemented.

  4. Columnstore Index: This is a technology for storing, retrieving, and managing data by using a columnar format, called a columnstore.

  5. Full-text Index: This is a special type of token-based functional index that is built and maintained by the Full-Text Engine for SQL Server.

Why Indexing?​

The main purpose of indexing is to enhance the performance of SQL queries. It reduces the number of disk I/O (input/output) operations, which ultimately results in faster reading times. However, indexes also have a downside: they need storage space, and they can slow down the performance of write operations (like insert, update, and delete) because the system also needs to update the index.

When to use Indexes?​

Here are some situations where indexing can be beneficial:

  • The database table is large.
  • There are frequent, complex queries on the table that return a small percentage of data.
  • The columns are often used for searching and sorting the data.
  • The columns contain a high number of distinct values.

Creating an Index​

Here's an example of how to create an index:

CREATE INDEX index_name
ON table_name (column1, column2, ...);

Conclusion​

In summary, indexing is a powerful way to optimize the performance of SQL queries. However, it's important to use them judiciously as they can consume significant storage space and slow down the performance of write operations. Always remember that the goal of indexing is to strike a balance between read and write operations to achieve overall performance efficiency.

Remember, SQL performance tuning is a broad topic and this tutorial just scratched the surface. Continue exploring and practicing with different aspects of SQL to become more proficient!