For T-SQL Tuesday< #65, I give a little detail on something I learned this week about altering a column from NOT NULL to NULL.

A little advice on the use of MDF/LDF files for backups.

Tip : Prevent and log certain login attempts

I discuss the benefits of explicitly referencing columns in a query.

I follow up on a question from a triggers presentation at SQLBits, addressing the impact of trigger overhead for T-SQL Tuesday.

I show DDL commands in Azure SQL Database that can now run as online operations instead of blocking, size-of-data operations.

I address a popular theory that NOLOCK can substantially reduce locking overhead against #temp tables.

Tip : Give SQL Server users access to Extended Events

I talk about a couple of subtleties of THROW, and how to avoid frustrating bouts of troubleshooting.

I describe a scenario where Common Criteria compliance was deemed the cause of high LCK_M_SCH_M waits for multiple customers.

I show some views I use to make metadata queries simpler.

I show how to use common table expressions (CTEs) to better optimize SQL Server pagination queries that use OFFSET / FETCH.

I examine various impacts on SQL Server – not just disk space – when choosing a GUID as a clustering key.

I walk through several potential causes for different plans and/or performance for the same database on two "identical" servers.

Tip: Finding views with (or without) a certain property

I discuss a handful of reasons "identical" queries might yield multiple plans, contributing to plan cache bloat.

Tip: Over 40 queries to find tables with or without a certain property

Tip : Verify the databases a login can see – and why

I show some tricks for getting row counts efficiently, and explain why an accurate row count for a large table is a pipe dream.

I repeat "Bad habits" advice from the past about using statement terminators and schema references to avoid debugging troubles.

I demonstrate an affordable approach to readable secondaries, without the need for Availability Groups and all the licensing costs involved with Enterprise Edition and Software Assurance.

Tip : Map between SQL Server SIDs and Windows SIDs

I point out that an often-used connection setting, AttachDBFileName, may be the source of many wasted hours of debugging and troubleshooting.

In this tip, I show how to use dynamic SQL to drop and re-create all foreign keys.

I treat a common scenario: behavior differs between two SQL Server databases that may be the same version, but different compatibility levels.

Tip : What Effect Does Persisting a Computed Column Have in SQL Server?

I discuss the NOLOCK hint in SQL Server, and why you want to avoid slapping it onto every table mentioned in every query.

Tip : What Happens When a Computed Column is Persisted in SQL Server?

I discuss examples where people expect SQL Server to perform tasks that really should be performed outside the scope of the database.

Tip : Change All Computed Columns to Persisted in SQL Server

I discuss ten common cases of misplaced optimization.

Tip : SQL Server Video – Tricks to play on your DBA – 2

I explain why you should avoid helper functions, and join against the catalog views instead.

I provide four real-world examples where grouped concatenation allows you to avoid the monotony of cursors and while loops.

I take a closer look at some additional requirements for typical grouped concatenation queries in SQL Server.

Tip : SQL Server Video – Tricks to play on your DBA – 1

I use a T-SQL Tuesday theme to demonstrate a use case for the SQL_VARIANT data type that you may not have considered: Conditional ORDER BY.

I show the safest and most efficient ways to perform grouped concatenation in SQL Server.

Tip : Why the SQL Server FORCESCAN hint exists

This month's T-SQL Tuesday is about assumptions in SQL Server.

Following a recent update, I take a first look at a new performance enhancement and trace flag (2453) aimed at improving cardinality estimates for table variables and table-valued parameters.

I look at some unexpected behavior with the CASE expression and some of its derivatives.

Tip : Connect to SQL Servers in another domain using Windows Authentication

Tip : Choosing Between SQL Server 2012 and SQL Server 2014

I take a closer look at the overhead of using Extended Events to track the creation of #temp tables.

I show how you can use Extended Events to track temp table creation and identify which session created which #temp table.

I describe the new SQL Server 2014 feature, Delayed Durability, and put it through its paces.

Tip : Get more info about failed logins using Extended Events