SQL Server is a feature-rich relational database management system, and it’s no surprise that some of its features are more popular than others. However, there are times when certain features may be overused, potentially leading to less efficient implementations or missed opportunities for optimization. In this blog post, we’ll explore three such Overutilized features.
1. Cursors
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 *
The 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
The 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.
Before using 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:Â Pinal Dave (https://blog.sqlauthority.com)
1 Comment. Leave new
While I generally agree that “SELECT *” is almost always undesirable, this is a case where I like to promote a tool from RedGate called “SQL Prompt”. Just one of its many features is its ability to take “SELECT * FROM table_name” and replace “*” with a formatted list of columns from the table.
As you have pointed out in the past, dragging the column list from the Object Explorer also drops a list of columns into your query. The list appears on a single line and every column is surrounded with square brackets. I usually end up copying the list to Notepad++, doing some mass edits, and then pasting the “prettified” result back into SSMS.
SQL Prompt allows each user to set up formatting rules for how the columns will be presented. For example, my office forbids the use of any table or column name that requires square brackets in order to be understood by the parser. This makes the square brackets almost always unnecessary. Further, I’ve configured my SQL Prompt to allow all the column names on one line only if that one line is 100 characters or less. Very few tables in my company’s principal database meet this requirement.
With a few keystrokes or a mouse click and the Tab key, I have a nice list of columns that I can then edit down to the actual columns I need for the specific task at hand.