The ‘aggregate concatenation’ T-SQL (anti-)pattern

Some time back, Dimitri Furman who works as a Senior Consultant in the Microsoft Services team shared a very useful tip. It pertains to a pattern of usage wherein strings from multiple rows are concatenated into a single large (typically comma delimited) string. The usual way that we see this being accomplished is by code…

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T-SQL ranking functions to the rescue once again!

This week I happened to assist with an internal application where there was a performance issue with a specific query. One of my observations with that query was that it was doing self-joins in order to determine the latest iteration of a specific record. That’s a common anti-pattern which can be fixed by using T-SQL’s…

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Common sub-expression elimination in SQL Server: what you need to know

In working with our customers, I come across some very interesting patterns in T-SQL. Not all of these patterns are complex on the face of it, but their impact can sometimes be substantial. Here is a simple example to demonstrate what I am referring to: select CASE WHEN EXISTS (SELECT * FROM Person.Person P where…

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Tracking TEMPDB internal object space usage in SQL 2012

It is a documented fact that using the MAX specifier can result in TEMPDB usage in specific cases. From the TEMPDB whitepaper, some of these can use ‘internal object’ space within TEMPDB: “all of the large object types: text, image, ntext, varchar(max), varbinary(max), and all others.” Now, a FAQ from our customers is how to…

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Normalizing T-SQL text, part 2: using the TransactSql.ScriptDom classes

Happy New Year 2014 to all of you! With SQL Server 2014 set to release this year, I’m sure you are all excited about the months to come. In my previous post I had reviewed the classic ways of obtaining ‘normalized’ text for ad-hoc SQL queries. Do take a minute to glance at that post…

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Normalizing T-SQL text, part 1: using the RML Utilities and the DMVs

A common problem when dealing with workloads which issue ad-hoc SQL commands (i.e. without parameterization) is to find out the ‘normalized’ version of the pattern. For example, these three statements are essentially the same ‘template’: SELECT BusinessEntityId FROM Person.Person WHERE LastName = ‘Smith’ SELECT BusinessEntityId FROM Person.Person WHERE LastName = ‘Singh’ SELECT BusinessEntityId FROM Person.Person…

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SQL PASS ScriptDom talk: Recording now available!

The SQL PASS AppDev team has uploaded the recording of my session. You can click on the embedded player to view the HD recording. And if you have not looked at the slides and demos, please do review my previous post which refers to those!

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XML ‘Visualizer’ for the TransactSql.ScriptDom AST

I’ve described the ScriptDom parser previously on this blog. The visitor pattern is great when you know exactly what you are looking for in the parse tree, but as you would have seen, due to the polymorphic nature of the ScriptDom classes, it is quite difficult for a truly generic tree walk when you don’t…

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PowerShell script to extract T-SQL task code from SSIS packages

Requirement Some time back I presented a PowerShell script which extracts T-SQL code from RDL files. Remember that I created this script to assist me in doing code reviews of ad-hoc SQL snippets which were embedded in the report definition files. Another common usage of ad-hoc T-SQL code is within SSIS packages, specifically the Execute…

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PowerShell script to extract T-SQL code from RDL files

One of the things I do in my day job at Microsoft Services is to review database design and T-SQL code. Now, when it comes to code, there is a challenge just to find ALL the possible code which hits our database engine. This is because a non-trivial amount of T-SQL code is not in…

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