SQL

Think about searching for a contact in your phone. You can either scroll through everything or jump straight to a specific letter. That’s basically the difference between regular database access and using covering indexes in SQL. They can make your queries run way faster, but many developers don’t know about them or use them properly. Let’s talk about what they are and when you should use them. What is a Covering Index? A covering index is simply an index that has all the columns your query needs, so the database doesn’t have to go back to the actual table. W ...

I’ve been writing SQL for years, and one thing I’ve noticed is how many developers stick with subqueries for everything. But Common Table Expressions (CTEs) can often make your code much cleaner and sometimes faster too. Let me show you when you might want to reach for a CTE instead. Understanding the Basics So what’s the difference? A subquery is just a query nested inside another query (query-ception, if you will), while a CTE is more like a temporary named result that you can reference in your main query. CTEs only stick around for the statement they’re in. ...

Let’s talk about two SQL operators I use all the time: EXISTS and IN. Both help filter records with subqueries, but they work quite differently behind the scenes. Getting this right can make your queries run much faster. How EXISTS and IN Work In simple terms, EXISTS checks if any matching rows exist, while IN compares a value to a list of results. Here’s what they look like in action: ...

Introduction to Table-Valued Parameters Ever needed to send a bunch of rows from your C# app to SQL Server but didn’t want to make dozens of separate calls? That’s where table-valued parameters come to the rescue. They let you package up multiple rows of data and send them to a stored procedure in just one trip to the database. SQL Server introduced this feature back in 2008, and it’s a game-changer compared to old approaches like building giant string commands, parsing XML, or making individual database calls for each record. ...

Introduction to Correlated Subqueries Ever run into a SQL problem where you need to compare each row with some calculation based on related data? That’s where correlated subqueries come in handy. These are special subqueries that reference columns from the outer query, essentially creating a link between the inner and outer parts of your query. What makes them different from regular subqueries is that they run once for each row the outer query processes. This makes them perfect for row-by-row operations where each calculation depends on the current row’s values. ...