Indexing

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Indexing

Indexed View Matching With GROUP BY And DISTINCT

Last Updated November 29, 2018

Bit Of A Kick I’ve been playing with indexed views a little bit lately for some demos in my Bits Precon. There are a whole bunch of limitations in creating indexed views. One of them is that you can’t base the query on DISTINCT. Fair enough, but you can do GROUP BY. And what’s pretty…

Indexed View Creation And Underlying Indexes

Last Updated November 29, 2018

Erik Darling

Indexing

Accidental Haha While working on some demos, I came across sort of funny behavior during indexed view creation and how the indexes you have on the base tables can impact how long it takes to create the index on the view. Starting off with no indexes, this query runs in about six seconds. Transact-SQL DECLARE…

Tales From Overindexing: Too Many One Column Indexes

Last Updated November 23, 2018

Erik Darling

Execution Plans, Indexing, SQL Server

Master Plan Sometimes you see a query, and it’s hitting one table, and then the query plan looks like a vase full of spaghetti. Usually, there’s a view involved. Usually. Sometimes, there’s just really weird indexing. Here’s A Thing, Look At It Promises This is a query against one table. No views, no functions, no…

Adventures In Foreign Keys 5: How Join Elimination Makes Queries Faster

Last Updated December 29, 2021

Erik Darling

Execution Plans, Foreign Keys

FINALLY… This is the last post I’ll write about foreign keys for a while. Maybe ever. Let’s face it, most developers probably find them more annoying than useful, and if you didn’t implement them when you first started designing your database, you’re not likely to go back and start trying to add them in. Depending…

Adventures In Foreign Keys 4: How to Index Foreign Keys

Last Updated December 29, 2021

Erik Darling

Execution Plans, Foreign Keys

This week, we’re all about foreign keys. So far, we set up the Stack Overflow database to get ready, then tried to set up relationships, and encountered cascading locking issues. Dawn Of The Data I don’t know how long the recommendation to index your foreign keys has been a thing, but I generally find it useful…

Adventures In Foreign Keys 3: Why Cascading Deletes Perform Slowly

Last Updated December 29, 2021

Erik Darling

Execution Plans, Foreign Keys, Locking, Blocking, and Isolation Levels

Legendreary In the last post, I looked at some issues with implementing foreign keys with cascading actions. Namely that, well, it fell apart pretty quickly just trying to set up. I didn’t even get to the point where I wanted to test all those relationships. But there’s an even worse surprise waiting for you if…

Adventures In Foreign Keys 2: Common Foreign Key Errors

Last Updated December 29, 2021

Erik Darling

Execution Plans, Foreign Keys

This week, we’re all about foreign keys. Yesterday’s post covered scripts to set up the Stack Overflow database to get ready, eliminating data that would violate FK relationships. You Had Two Jobs! Let’s say I wanted to implement Foreign Keys to do two things If a user deletes their account, all of their badges, comments, and…

Adventures In Foreign Keys 1: Setting Up Foreign Keys in Stack Overflow

Last Updated December 29, 2021

Erik Darling

Execution Plans, Foreign Keys

In A Foreign Key, In A Foreign Table Much of what people want from foreign keys, like referential integrity and join elimination, are only as guaranteed as much as SQL Server can trust your constraints (and even then…). The same goes for check constraints, too. Thankfully, things like Primary Keys and Unique Constraints are sort…

How Check Constraints MIGHT Improve Your Queries and Missing Index Requests

Last Updated October 31, 2018

Brent Ozar

Execution Plans, Indexing

The more SQL Server knows about your data, the better your query plans can get. Say you’ve got an app that’s designed to store multiple companies in a single database – but you don’t actually use it that way. All of the data in a given database is actually for the same company. We’ll use…

Filtered Indexes vs Parameterization (Again)

Last Updated October 21, 2018

Erik Darling

Execution Plans, Indexing

At First I Was Like… This won’t work at all, because parameters are a known enemy of filtered indexes. But it turns out that some filtered indexes can be used for parameterized queries, whether they’re from stored procedures, dynamic SQL, or in databases with forced parameterization enabled. Unfortunately, it seems limited to filtering out NULLs…

Batch Mode For Row Store: Does It Fix Parameter Sniffing?

Last Updated May 26, 2020

Erik Darling

Batch Mode, Execution Plans, Indexing, Parameter Sniffing

Snorting The Future SQL Server 2019 introduced batch mode over row store, which allows for batch mode processing to kick in on queries when the optimizer deems it cost effective to do so, and also to open up row store queries to the possibility of Adaptive Joins, and Memory Grant Feedback. These optimizer tricks have…