T-SQL

I was helping a client with a query, and I’m going to rework the example to use the Stack Overflow database for easier storytelling. Say we need to: Find all the locations where users have logged in since a certain date, then Return the total count of people who live in those locations One way…

When you write dynamic SQL, start like this: CREATE OR ALTER PROC dbo.MyProc AS BEGIN DECLARE @StringToExecute NVARCHAR(4000); SET @StringToExecute = N'SELECT /* MyProc */ '; ... 12345 CREATE OR ALTER PROC dbo.MyProc ASBEGIN DECLARE @StringToExecute NVARCHAR(4000); SET @StringToExecute = N'SELECT  /* MyProc */ '; ... Right after the SELECT (or INSERT or UPDATE or whatever),…

You’ve been working with Microsoft SQL Server for yeeears, and you’re pretty confident that you know how to write a query. So when I tell you about a book called T-SQL Fundamentals, you’re all, “nah, man, I got this covered.” You are incorrect. Sure, the first 5 chapters of the book are about 1-2 table…

In a programming language like C# or Java, you tell the computer what to do, in order. Get the customers from California, then get their invoices, then sum the total. SQL, on the other hand, is a declarative language where you declare the shape of your result set: Get the total sales from Californian customers.…

This week’s series on error handling has been an eye opener for many of us. We’ve laughed. We’ve cried. We’ve screamed in horror. We’ve read the documentation. I don’t blame you. This is a really confusing topic, and for many of us, it’s the first time we’ve actually looked at the mechanics of how transactions,…

CAN YOU BELIEVE THAT HOT MESS IN YESTERDAY’S POST?!? I know, right? You thought that by combining try/catch with a transaction, you’d get robust error handling.  Instead, you ended up with half the tables populated, and a leftover open transaction. You’d already forgotten Tuesday’s post in which I pointed out that TRY/CATCH doesn’t catch low…

In yesterday’s epic cliffhanger, you might have been shocked to discover that a plain ol’ transaction does not solve our problem – and in fact, it makes things worse. With yesterday’s code, we still got rows inserted into the Parent table, no rows in the Child table, and a nasty surprise that our session will…

Let’s say we have two tables, Parent and Child, and we need to guarantee that they both get populated at once. We’ll write a single stored procedure to do both inserts: DROP TABLE IF EXISTS dbo.Parent; DROP TABLE IF EXISTS dbo.Child; CREATE TABLE dbo.Parent (ID INT IDENTITY(1,1), DateAdded DATETIME2); CREATE TABLE dbo.Child (ID INT IDENTITY(1,1),…

David Tovee asked a great question in yesterday’s Mastering Query Tuning class. He asked his fellow students, “How many of you actually use TRY/CATCH?” I turned it into a Twitter poll because I wanted to check a wider audience: When the developers at my company write new queries, they use TRY/CATCH and exception handling: —…

When you’re working with T-SQL, you’ll often see SET NOCOUNT ON at the beginning of stored procedures and triggers. What SET NCOUNT ON does is prevent the “1 row affected” messages from being returned for every operation. I’ll demo it by writing a stored procedure in the Stack Overflow database to cast a vote: CREATE…

It’s hard to set absolute rules about, “Feature X should absolutely never be used.” However, there are some features that set off alarm bells when I see them. Usually, when I start asking more questions about when we’re using those particular features, I get answers of, “Oh, I didn’t know that was a problem.” As…

There are two ways you can write comments in T-SQL: --By starting a line with two dashes, or /* By framing it on both sides like this */ 123 --By starting a line with two dashes, or /* By framing it on both sides like this */ Never, ever use two dashes. Never. The problem is that…

T-SQL Tuesday is a monthly blogothon where we get together and write about a different topic. I’m hosting this month’s episode. Your mission: write a blog post about your favorite data type, and schedule it for next Tuesday, March 9. Mad about money? Feverish about float? Tell us what you use your favorite data type…

You’ve got a staging table with millions of rows, and you want to join that over to a production table and update the contents. However, when you try to do it all in one big statement, you end up with lock escalation, large transaction log usage, slow replication to Availability Groups, and angry users with…

Say you’ve got a two-step process where you’re: Inserting rows into a table that has an identity column, then Querying that table to figure out what identities you got There’s a a faster way that doesn’t require hitting the table twice: the OUTPUT clause. I’ll demonstrate it with the Badges table from the Stack Overflow…

When your query has a scalar user-defined function in it, SQL Server may not parallelize it and may hide the work that it’s doing in your execution plan. To show it, I’ll run a simple query against the Users table in the Stack Overflow database. SELECT TOP 100 DisplayName, Location, Reputation, Id FROM dbo.Users ORDER…

SQL Server’s full text search is amazing. Well, it amazes me at least – it has so many cool capabilities: looking for prefixes, words near each other, different verb tenses, and even thesaurus searches. However, that’s not how I see most people using it: I’ve seen so many shops using it for matching specific strings,…

In yesterday’s blog post about using triggers to replace computed columns, a lively debate ensued in the comments. A reader posted a trigger that I should use, and I pointed out that their trigger had a bug – and then lots of users replied in saying, “What bug?” I’ll demonstrate. We’ll take the Users table…