Last week we looked at identifying object dependencies through performing a wildcard search on the objects such as procedures. I noted another option could be to use the views such as sys.sql_expression_dependencies and Kevin also commented about using the supporting functions such as sys.dm_sql_referencing_entities. I wanted to briefly look at both of these options and look at how their results can […]
When looking to migrate, consolidate or deprovision parts of a SQL solution it’s key to understand the dependencies on the objects inside. Identifying dependencies can be challenging and I wanted to demonstrate one way to approach this. We’ll start with some objects across a couple of databases: The simplest option to find references within a […]
Dynamic SQL has many uses and one of these can help us fix Parameter Sniffing issues. Here we’ll look at how it can be used to generate multiple execution plans for the same query. Parameter sniffing is a common issue. Even for simple queries we can run into suboptimal plans being produced. There are multiple ways we […]
When building dynamic SQL, safety is crucial. As we saw last week, we have the QUOTENAME function which can help when referencing object names. Another aspect to consider is use of parameters. Integrating them incorrectly can leave us vulnerable to SQL injection attacks. Let’s take a look at how to handle them the wrong way, followed by the right […]
In the last post we looked at how TOP and MAX operators compared. We saw the execution plan for a MAX function used a Stream Aggregate operator which is one of two which we can use for aggregation I wanted to look at the two operators and how they perform the same tasks in different ways. The way they function is key […]
Both TOP (1) and MAX can be used to identify the largest value in a data set. Whilst they get the same result it isn’t necessarily in the same way. Firstly, what is the difference between the two? The TOP clause limits the number of results which are returned from a query, in this instance we’re focussing on a single result. […]
A Trivial plan is created when SQL Server really doesn’t have any choice in how it’s going to execute. Here’s an example from the StackOverflow database with the indexes removed: There really isn’t any choice but a clustered index seek. It’s the only index and its about as effective as we can get given we’re filtering on […]
The DISTINCT clause in a query can help us quickly remove duplicates from our results. Sometimes it can be beneficial to stop and ask why. Why do we need to use the clause, why are we receiving duplicates from our data? I see this typically due to a JOIN being used where we don’t really want all of those results. This could […]
Deadlocks are an enduring feature of SQL Server. They’ve been a source of pain for many over the years and there are various ways to diagnose, mitigate or resolve them. Here I want to demonstrate approach I haven’t seen discussed – using an application lock to segregate processes. An example where I’ve used this effectively […]
In the previous post we looked at the functions TRY_CAST, TRY_CONVERT, and TRY_PARSE and how they compared. I wrapped up and said that my preference for new developments would be to use TRY_PARSE due to the tighter control which it provides us. As with everything in SQL Server however, there is no ‘best’ approach, it depends. I therefore wanted […]
Andy Brownsword 