T-SQL

Hell Here! Get Your Fresh Hell, Here! Let’s face it — as far as developer tools go, SSMS is pretty bad. Intellisense? The jokes write themselves. Don’t get me wrong, SSMS is a good management tool, but it’s not a good development tool (and what kind of maniac sticks debug — F6 — next to execute —…

How to Get a Random Row from a Large Table

Last Updated March 7, 2018

Method 1, Bad: ORDER BY NEWID() Easy to write, but it performs like hot, hot garbage because it scans the entire clustered index, calculating NEWID() on every row: The plan with the scan That took 6 seconds on my machine, going parallel across multiple threads, using tens of seconds of CPU for all that computing…

Fifteen Things I Hate About ISNUMERIC

Last Updated February 26, 2018

Yello! Transact-SQL SELECT ISNUMERIC('$') AS [What] UNION ALL SELECT ISNUMERIC('£') AS [What] UNION ALL SELECT ISNUMERIC(',') AS [What] UNION ALL SELECT ISNUMERIC('.') AS [What] UNION ALL SELECT ISNUMERIC('0e+99') AS [What] UNION ALL SELECT ISNUMERIC('2e2') AS [What] UNION ALL SELECT ISNUMERIC('12D4') AS [What] UNION ALL SELECT ISNUMERIC(',1,1,1,1,1,1,1') AS [What] UNION ALL SELECT ISNUMERIC('-') AS [What] UNION…

Using WITH (NOEXPAND) to Get Parallelism with Scalar UDFs in Indexed Views

Last Updated February 12, 2018

Scalar functions are the butt of everybody’s jokes: their costs are wrong, their STATS IO results are wrong, they stop parallelism when they’re in check constraints, their stats are wrong in 2017 CU3, they stop parallelism in index rebuilds and CHECKDB, I could go on and on. Recently, we ran across yet another scenario where…

Creating Insert Triggers to Silently Ignore Data You Don’t Want

Last Updated February 1, 2018

Bad Idea Jeans, T-SQL

Say you’ve got an application that insists on inserting data into the database, and…you don’t want the data. You want the application to THINK it inserted the data – you don’t want to roll it back or return an error to the end user. You just don’t want the data, and you don’t want the…

Using LIKE on Integers Gets You Implicit Conversion

Last Updated February 1, 2018

Using the Stack Overflow public export, take these two queries looking for a particular user by Id (the clustering key): Transact-SQL SELECT * FROM dbo.Users WHERE Id = 26837; SELECT * FROM dbo.Users WHERE Id LIKE 26837; 12 SELECT * FROM dbo.Users WHERE Id = 26837;SELECT * FROM dbo.Users WHERE Id LIKE 26837; The first…

Two Code Patterns That Don’t Virtualize Well

Last Updated January 19, 2018

Virtualization used to be a really Big Deal™ for database admins: we had to do a lot of careful planning to get a virtualization project done right. These days, virtualization is more and more of a no-brainer: most apps make the transition just fine. Every now and then, though, an exception pops up – usually…

#TSQL2sday: Brad McGehee Made a Difference in My Career.

Last Updated November 8, 2017

For this month’s T-SQL Tuesday, Ewald asked who’s made a difference in our careers. When I first got started out in SQL Server, all I had was books and Books Online. Back then, neither of them were particularly well-indexed, nor were they up to date. Then I found a web site that turned things around.…

SQL Server Workarounds

Last Updated October 12, 2017

Development, SQL Server, T-SQL

360 Questions We’ve been asking you folks a lot about what you’d add to SQL Server, and we’ve gotten some great answers. There are even some that have been answered in the last couple versions of SQL Server. For instance, 2016 brought us STRING_SPLIT! SQL Server 2017 has a whole bunch of neat stuff: CONCAT_WS…

Bad Idea Jeans: Multiple Index Hints

Last Updated May 23, 2017

Bad Idea Jeans, T-SQL

I hate that you can do this Here’s the thing: I’m mostly writing this because I didn’t know you could do it. But it’s cool, because it’ll reinforce some other concepts, and I’ll show you why you shouldn’t do it. I’m talking, of course, about index hints. To be more specific, hinting multiple indexes on…

Don’t Use Scalar Functions in Views.

Last Updated May 1, 2021

The short story: if your view has a scalar user-defined function it it, any query that calls the view will go single-threaded, even if the query doesn’t reference the scalar function. Now for the long story. Quite often people will inherit and rely on views written back in the dark ages, before people were aware…

Announcing Erik’s First Video Class: T-SQL Level Up, Level 2

Last Updated April 23, 2017

Company News, T-SQL

You’re confident writing queries to get the data you want, and you’ve been doing it for a couple of years. You’ve taken our free T-SQL Level Up class, mastered tally tables and windowing functions, but what else is there? In this class with T-SQL maestro Erik Darling, you’ll learn tricks to take your queries to…

Replacing ISNULL In A WHERE Clause

Last Updated April 7, 2017

Execution Plans, T-SQL

I like blogging Really, I do. But sometimes I like a change of pace. Instead of blogging about this question, I posted it over on dba.stackexchange.com. Also, I thought it was an interesting question, and apparently many other people agreed. Not just because I wanted some more points, but because blog comments are notoriously sucky…

The Surprising Behavior of Trailing Spaces

Last Updated April 11, 2017

In every training class we do, I learn stuff from students. Here’s last week’s surprise. Create a temp table, and put in a value with trailing spaces. Then query for it using the = and <> operators, using different numbers of trailing spaces: Transact-SQL CREATE TABLE #Wines (Winery VARCHAR(50)); INSERT INTO #Wines VALUES ('Cliff Lede…

Fun With Logging Dynamic SQL

Last Updated April 7, 2017

While working on a demo I thought this might make a fun aside to share on the blog, because working with dynamic SQL can be challenging. Especially if you don’t have a monitoring tool or application profiling to figure out who ran what and when, most of the time you’ll have no idea what went…

sp_BlitzCache Tip: Cutting Through Heavy Dynamic SQL Use

Last Updated November 16, 2017

First Responder Kit, sp_BlitzCache, T-SQL

It keeps me up at night Out of the box, sp_BlitzCache will give you enough stuff to work on in your server’s plan cache to last a month of leap days. This is great for most people, but if you use a ton of dynamic SQL in stored procedures, it can make things difficult. What’s…

No seriously, don’t use SQL_VARIANT for that

Last Updated March 9, 2017

Development, T-SQL

I’d been meaning to write this for a while I half-stumbled on the weirdness around SQL_VARIANT a while back while writing another post about implicit conversion. What I didn’t get into at the time is that it can give you incorrect results. When I see people using SQL_VARIANT, it’s often in dynamic SQL, when they don’t…

Inline Table Valued Functions: Parameter Snorting

Last Updated May 26, 2020

Parameter Sniffing, SQL Server, T-SQL

You’ve probably heard about parameter sniffing But there’s an even more insidious menace out there: Parameter Snorting. It goes beyond ordinary parameter sniffing, where SQL at least tried to come up with a good plan for something once upon a compile. In these cases, it just plain gives up and throws a garbage number at…

High Compiles and Multi-Statement Table Valued Functions

Last Updated February 14, 2017