What is a Savepoint in SQL?

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When working with databases, there’s a good chance you’ve had to deal with transactions. Transactions are those “all or nothing” blocks of work that make sure your data stays consistent. But what happens if you’re halfway through a transaction and realize that only part of it needs to be undone, not the whole thing? That’s where savepoints can help.

In SQL, a savepoint is basically a checkpoint you can set inside a transaction. It lets you roll back to that specific point if something goes wrong, without undoing everything that came before it. If something gets messed up, you can load your last save instead of starting again from scratch.

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SQL Server UNPIVOT Explained

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Sometimes you need to do the reverse of pivoting – take data that’s spread across multiple columns and convert it back into rows. You might receive data in a wide format from Excel, need to normalize denormalized data for storage, or simply need to reshape data for a different type of analysis. Fortunately, SQL Server has the UNPIVOT operator which is designed for this very scenario.

Whereas PIVOT transforms rows into columns, UNPIVOT transforms column headers back into row values. This creates a narrower, longer dataset from a wide one.

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What is a MERGE Statement in SQL?

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The MERGE statement is SQL’s convenient tool for synchronizing data between two tables. It lets you perform INSERT, UPDATE, and DELETE operations in a single statement based on whether matching records exist. Instead of writing separate logic to check if a record exists and then deciding what to do with it, MERGE handles all of that in one go.

Most major database systems support MERGE, including SQL Server, Oracle, and DB2. PostgreSQL added native MERGE support in version 15, but if you’re on an older version, you can use INSERT … ON CONFLICT as an alternative. MySQL doesn’t have MERGE but offers INSERT … ON DUPLICATE KEY UPDATE for similar functionality.

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How to Enable Query Store in SQL Server

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Query Store is SQL Server’s built-in query performance tracking system that captures execution history, plans, and runtime statistics. From SQL Server 2022 it’s enabled by default for all newly created databases. But in earlier versions, it’s disabled by default, which means you’ll need to explicitly enable it on each database where you want to track query performance.

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What is Parameter Sniffing in SQL Server?

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Parameter sniffing is a feature in SQL Server where the query optimizer examines (or “sniffs”) the parameter values the first time a stored procedure or parameterized query executes. It uses these specific values to create an execution plan optimized for those particular parameters. The plan is then cached and reused for subsequent executions, even when different parameter values are passed in.

This behavior can be efficient if the initial parameters are representative of typical queries, but it can also cause performance problems if later calls use very different parameter values that make the cached plan inefficient. 

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How PIVOT Works in SQL Server

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In SQL databases, a pivot operation transforms rows into columns, making it easier to summarize or compare data across categories. It’s commonly used to convert long, vertical datasets into a wider, more readable format. For example, turning a list of monthly sales records into a table where each month becomes its own column.

By applying aggregation functions like SUM(), COUNT(), or AVG() during the pivot, SQL can reorganize and summarize data for reporting or analysis.

In this article, we’ll take a look at SQL Server’s PIVOT operator, which is designed specifically for pivot operations.

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What is the Query Store in SQL Server?

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Query Store is SQL Server’s built-in query performance tracking system. It captures a history of queries, their execution plans, and runtime statistics, storing everything in the database itself. It constantly records what’s happening so you can analyze performance issues after the fact.

Query performance issues can be notoriously hard to debug. A query runs fine for weeks, then suddenly it’s slow, and by the time you check, the problem has vanished or the execution plan is no longer in cache. SQL Server 2016 introduced Query Store to address this. Once enabled on a database, it continuously records query execution history, giving you the data you need to investigate performance problems after they happen. It won’t tell you what’s wrong or how to fix it, but at least you’ll have evidence to work with instead of flying blind.

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