Choosing the Right Indexing Strategy: Clustered vs Non-Clustered Indexes

When deciding whether to use a clustered or non-clustered index in a database, there are a few factors to consider:

Table size and data distribution: If the table is relatively small, a clustered index may not provide significant benefits, and a non-clustered index may be sufficient. On the other hand, if the table is very large, a clustered index can help improve query performance by reducing the number of disk reads required to retrieve data. Additionally, if the data in the table is uniformly distributed, a clustered index may be more beneficial than a non-clustered index.
Data modification frequency: Tables with frequent data modification operations such as inserts, updates, and deletes may benefit from a non-clustered index over a clustered index. This is because a clustered index requires reorganizing the data on disk, which can be time-consuming and resource-intensive. Non-clustered indexes, on the other hand, are generally quicker to create and update.
Query patterns: The type of queries that will be run against the table is also an important consideration. Queries that commonly use the same column(s) for filtering or sorting may benefit from a non-clustered index. Queries that frequently access all the columns in a table or require sorting by multiple columns may benefit from a clustered index.
Primary key or unique constraints: A table must have a clustered index if it has a primary key or unique constraint. In this case, the primary key or unique constraint is used to create the clustered index, and a non-clustered index can be created on other columns.

In summary, a clustered index is useful for large tables with uniform data distribution and queries that frequently access all columns or require sorting by multiple columns. A non-clustered index is useful for smaller tables with frequently modified data or queries that frequently filter or sort by specific columns. Ultimately, the decision to use a clustered or non-clustered index will depend on the specific characteristics of the table and the queries that will be run against it.