The Clustered Index Is Vital To Your Database Design

Azure, SQL Server, SQL Server 2016
This is post #9 supporting  Tim Ford’s (b|t) initiative on #iwanttohelp, #entrylevel. Read about it here. You get one clustered index per table. That bears repeating, you get one clustered index per table. Choosing a clustered index is an extremely important and fundamental aspect of all your SQL Server work. The one clustered index that you get determines how the data in your table is stored. Because the clustered index determines how your data is stored, it also determines how your data is retrieved. Much of SQL Server is engineered around the clustered index because it is such a foundational object for the rest of all behavior. Without a clustered index, the data in your table is stored in what is called a heap. It is essentially a pile, a heap, of data,…
Read More

Constraints and SELECT Statements

Azure, SQL Server, T-SQL
I've posted previously about how a foreign key constraint can change how a SELECT query behaves. Logically that just makes sense. But other types of constraints don't affect execution plans do they? Yes. Let's take this constraint as an example: [crayon-5b63d99e9c19a767112107/] That will ensure that no values less than zero can slip in there. We can even validate it: [crayon-5b63d99e9c1aa626771880/] Will give me an error: Msg 547, Level 16, State 0, Line 470 The INSERT statement conflicted with the CHECK constraint "CK_SalesOrderDetail_UnitPrice". The conflict occurred in database "AdventureWorks2014", table "Sales.SalesOrderDetail", column 'UnitPrice'. Let's look at a SELECT query now. If we run this: [crayon-5b63d99e9c1af817857174/] The resulting execution plan looks like this: But, if I modify the query to look like this, adding an additional AND filter on the constrained UnitPrice…
Read More

Database Design Process

Misc, Tools
Buck Woody recently asked a question; how do you design a database. He outlined the process he followed and asked four questions about how each of us do our work: What process do you follow? How important are the business requirements? What tool do you use to create the design, do you need it to diagram, do you even care about diagrams? What's your biggest pain-point about designing? Funny enough, I haven't done a full on database design in over a year. My company just finished about 6 years of very hard-core engineering work, designing and building or redesigning and building, the majority of our data input and collection systems. Then, I was doing lots of design work. Now, we're either largely in maintenance mode for most of those systems, or the…
Read More