23Jul 2018 by Grant Fritchey 5 Comments

Database Fundamentals #18: The SELECT Statement

Database Fundamentals
In my previous Database Fundamentals post, I showed you how to use the Query Designer to build a query. That was a SELECT statement. The basic construct of all your SELECT statements will be the same. You’re going to define a list of columns, the table or tables you’re interested in, and some sort of filter criteria. That’s the bare bones basics of how it works. But, as we all know, the devil is in the details. There are lots and lots of details. This section will introduce the T-SQL SELECT statement and start explaining some of those details. Column List You’ve been introduced to the basic concepts of the column list in the SELECT statement. It represents the information that is going to be available for display by whatever…
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06Apr 2015 by Grant Fritchey 8 Comments

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: ALTER TABLE Sales.SalesOrderDetail WITH CHECK ADD  CONSTRAINT CK_SalesOrderDetail_UnitPrice CHECK  ((UnitPrice>=(0.00))) That will ensure that no values less than zero can slip in there. We can even validate it: INSERT Sales.SalesOrderDetail (SalesOrderID, CarrierTrackingNumber, OrderQty, ProductID, SpecialOfferID, UnitPrice, UnitPriceDiscount, rowguid, ModifiedDate ) VALUES (60176, -- SalesOrderID - int N'XYZ123', -- CarrierTrackingNumber - nvarchar(25) 1, -- OrderQty - smallint 873, -- ProductID - int 1, -- SpecialOfferID - int -22, -- UnitPrice - money 0.0, -- UnitPriceDiscount - money NEWID(), -- rowguid - uniqueidentifier GETDATE() -- ModifiedDate - datetime ); Will give me…
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