t-sql

How to View Query Execution History Over Time in SQL Server

by

In SQL Server, Query Store aggregates performance statistics into time intervals, allowing you to see how query performance changes over time. This historical view helps you identify when performance degraded, spot patterns like daily or hourly spikes, and correlate performance changes with deployments or data changes.

This assumes that Query Store is enabled on the database in question. So assuming Query Store is enabled on the database, you can use the following queries to check the execution history of queries over time.

Read more

What is a Missing Index in SQL Server?

by

SQL Server has a concept of “missing indexes”. And no, it’s not referring to an index that used to be there but has now disappeared. Rather, the missing index concept is designed to help us improve the performance of our database.

A missing index is an index that doesn’t yet exist on your table but probably should. SQL Server actually tracks queries that would benefit from indexes and stores suggestions in a set of dynamic management views (DMVs) called the missing index DMVs.

When you run a query and the optimizer thinks that this would be way faster with an index on those columns, it logs that suggestion. Over time, these suggestions accumulate, giving you a prioritized list of indexes that could improve your database’s performance.

Read more

Using DATEDIFF() with LEAD() to Calculate Time Until Future Events

by

When you’re analyzing how events unfold over time in a SQL database, one of the biggest challenges can be efficiently comparing what’s happening now to what comes next. Each event typically appears as its own row with a timestamp, but meaningful insight often comes from understanding how those timestamps relate to one another. Fortunately SQL Server provides some useful tools for this kind of sequential analysis.

Rather than relying on bulky self-joins or multi-step logic, SQL window functions offer a streamlined way to track these transitions. For example, by pairing the LEAD() function with DATEDIFF(), you can instantly measure the gap between consecutive events and surface insights that would otherwise require far more complex queries.

Read more

How to Unforce a Query Execution Plan in SQL Server

by

When you’ve forced an execution plan in SQL Server’s query store and later want to allow the optimizer to choose plans freely again, you’ll need to unforce the plan. You might want to do this because you’ve fixed the underlying issue or the forced plan is no longer optimal. Whatever the reason, the solution is straightforward and easy.

Read more

Generating Staggered Dates with SQL Server Window Functions

by

SQL Server’s window functions open up some creative possibilities when you need to work with dates. One interesting pattern involves pairing DATEADD() with ROW_NUMBER() to automatically generate sequential dates based on your query results.

This technique gives you a flexible way to calculate dates dynamically without hardcoding values or maintaining separate date tables. This can be useful for doing things like building a scheduling system, creating test data with realistic timestamps, or just spacing events across a timeline.

Read more