intro
Unlock the full power of SQL window functions with our comprehensive guide — dig into them and start learning today!
Every developer and DBA has come across situations where they need to solve problems by using functions. Still, functions are not all made the same and that’s especially the case in regards to your databases.
SQL has many functions available for you to peruse and we’re confident enough to say that many of them will be familiar to you. However, SQL window functions may be something different altogether.
Dig into them with us!
Introducing SQL Window Functions
In SQL, functions are used to complete a task that is usually predefined. Instead, SQL window functions perform calculations across a set of rows in a table that are somehow related to a row they’re acting on. In other words:
Window functions in SQL become a necessity once we find ourselves performing calculations needing a specific context.
Using SQL Window Functions: Example Usage
Performing calculations that need context means that SQL window functions will be defined with the SQL OVER() function and will be often combined with the SELECT query type, meaning that most of the time, they’d look like so:
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SELECT col_name,
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window_function(col_name2) OVER (...) AS new_col_name
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FROM table_name;
The SQL OVER() window function takes one or two arguments, them being PARTITION BY [something] or ORDER BY [something], meaning that the function will provide a constant value based on a calculation. Here’s an example:
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SELECT product_name, stock_amount,
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AVG(price) OVER(PARTITION BY product_name) AS avg_price
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FROM products;
SQL window functions may be especially useful if we're trying to rank something (RANK() is perhaps the simplest window function available), calculate the sum (SUM()) or an average value (AVG()) of something or differentiate between a number and an average number (number - AVG(number)) or perform related operations.
At the same time, they’re far from a holy grail: window functions will only be useful if we need to perform calculations across a set of rows and need a constant value based on a column or two. Otherwise, we’d be looking at other approaches like triggers, temporary tables, or even parameterized queries.
SQL Clients to the Rescue
One of those approaches may be related to SQL clients or other appliances that help us deal with our database infrastructure. Not all databases are made the same — and not all problems strike in the same way either.
You may be well-versed as far as the documentation of your beloved DBMS is concerned, however, things can quickly turn the other way and you will be facing problems you haven’t even heard of.
Here’s where SQL clients step in — with a SQL client like DbVisualizer by your side, you will always be sure that you’re in good hands because:
What you see above is just a small part of what DbVisualizer can provide to you, your employees, or your colleagues: its feature set is so extensive that we could write an entire book on it (we did write a book already — it’s just that it’s not about DbVisualizer), so you’d be better off checking them out yourself. Or, better yet, convince your boss to gain access to the tool after trying it out — you know, having another DBA by your side for a small price never hurts, right?
Summary
SQL window functions are functions that you can apply to your use case once you have to perform calculations on a set of rows. Such functions will act together with a function that performs a specific task to return a constant based on a column value. If you’ve read through this blog, you know exactly what this means — and how you can put it all to use.
Start putting it all to use today, read a book or two about optimizing your databases in the process while you familiarize yourself with DbVisualizer, and until next time.
FAQ
What are SQL window functions?
SQL window functions are functions perused by your database that perform calculations based on rows existing in a table. These kinds of functions return a value by looking at rows and mix them with the function specified by the user.
How to use SQL window functions?
SQL window functions can be utilized by using the OVER function combined with the PARTITION BY [something] or ORDER BY [something] clauses.
Where can I learn more about database performance?
To learn more about database performance, security, or other topics, consider mingling around the database community by attending conferences or gatherings, reading blogs, or staying on top of things by reading a book or two.
We recommend a book by Lukas Vileikis - it’s called Hacking MySQL: Breaking, Optimizing, and Securing MySQL for Your Use Case and it will help you understand how your databases break (or how you already broke them without even thinking about it), optimize your SQL query performance and database internals, and secure your database infrastructure for the future. Until then — au revoir.
