Cursors in SQL Server allow you to fetch rows and perform operations on each row individually. While cursors can be helpful in certain situations, they are often overused in places where a set-based function would be more efficient.
Cursors process rows individually, which can be much slower than set-based operations that process multiple rows simultaneously. Over-reliance on cursors can lead to performance issues, particularly with large datasets.
Before reaching for a cursor, it’s worth considering if the same result can be achieved with a set-based operation such as a JOIN or a subquery.
2. SELECT *
SELECT * command is a convenient shortcut to retrieve all columns from a table. However, it’s a feature that’s often overused, leading to unnecessary data retrieval and performance issues.
When you use
SELECT *, SQL Server has to retrieve every column from the table, even those you don’t need for your query. This can consume more CPU, memory, and I/O resources than necessary, particularly with wide tables.
Instead of using
SELECT *, it’s usually better to explicitly list the columns you need. This can significantly reduce the amount of data retrieved and improve query performance.
3. NOLOCK Hint
NOLOCK Hints in SQL Server allow you to read uncommitted data. This can be useful when performance is a priority and data accuracy isn’t critical. However,
NOLOCK is often overused, leading to potential data inconsistency issues.
When you use
NOLOCK, your query can read data that hasn’t been committed yet and might be rolled back later, leading to “dirty reads”. It can also lead to other phenomena like non-repeatable and phantom reads.
NOLOCK, consider if the potential performance gains outweigh the risks of reading inconsistent data. Other concurrency control techniques or isolation levels might be more appropriate in many cases.
Conclusion – Overutilized Features
While these overused features can certainly be helpful in the right situations, it’s essential to understand their implications and to use them judiciously. By broadening our understanding of SQL Server’s capabilities, we can make more informed decisions about which features to use and when.
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Reference: Pinal Dave (https://blog.sqlauthority.com)