Query Exercise: Why Are These 3 Estimates So Wrong?
Our prior Query Exercise introduced SQL Server’s 201 buckets problem: its inability to accurately estimate rows for more […]
Query Exercises
Query Exercise Answers: Solving the 201 Buckets Problem
In this week’s Query Exercise challenge, I explained SQL Server’s 201 buckets problem. SQL Server’s statistics only handle […]
Query Exercise: Solving The 201 Buckets Problem
When you run a query, SQL Server needs to estimate the number of matching rows it’ll find – […]
Query Exercise: What Makes SELECT TOP 1 or SELECT MAX ...
These two queries both get the same answer from the Stack Overflow database: SELECT TOP 1 LastAccessDate FROM […]
Query Exercise: Fix This Computed Column.
Take any size of the Stack Overflow database and check out the WebsiteUrl column of the Users table: […]
Query Exercise: Beat ChatGPT at Finding Good Question Times
What are the best days of the week and times of the day to post a question at […]
Query Exercise: Who’s Changing the Table?
For this week’s Query Exercise, your challenge is to find out who keeps messing up the rows in […]
Query Exercise: Finding Sister Locations to Help Each Other
For this week’s query exercise, let’s start with a brief query to get a quick preview of what […]
Query Exercise: Find Recent Superstars
For this week’s Query Exercise, we’re working with the Stack Overflow database, and our business users have asked […]
Query Exercise: Finding Long Values Faster
Our developers have come to us with a problem query that isn’t as fast as they’d like. Using […]
Query Exercise: Improving Cardinality Estimation
Your challenge for this week is to tune a query. Say Stack Overflow has a dashboard that shows […]
Query Exercise: Find Tagged Questions Faster.
For this week’s Query Exercise, we’re going to start with an existing query that has performance problems from […]
Query Exercise: Find the Best Time for Maintenance
If we’ve gotta take the database down for maintenance – perhaps a version upgrade, perhaps upgrading our own […]
Query Exercise: Find Posts with the Wrong CommentCount
For 2024, I’m trying something new: weekly homework challenges! For this week’s query challenge, we’re going to do […]
Find Foreign Key Problems: Answers & Discussion
Your Query Exercise was to find foreign key problems: data that might stop us from successfully implementing foreign […]
Query Exercise: Find Foreign Key Problems
For 2024, I’m trying something new: weekly homework challenges! For this week, let’s say we’ve decided to implement […]