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State Transition Constraints

Data Validation in a database is a lot more complex than seeing if a string parameter really is an integer. A commercial world is full of complex rules for sequences of procedures, of fixed or variable lifespans, Warranties, commercial offers and bids. All this requires considerable subtlety to prevent bad data getting in, and if it does, locating and fixing the problem. Joe Celko shows how useful a State transition graph can be, and how essential it can become with the time aspect added.

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The foreclosure issues that are occurring in the US might be due to database issues at one company. Steve Jones notes that when your database is the legal system of record, it has to be accurate.

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Question of the Day

Getting the Average

I have this data in the dbo.Commission table in a SQL Server 2022 database. 

salesperson commission
Brian       12
Brian       16
Andy        7
Andy        14
Andy        21
Steve       20
Steve       NULL
All the data is a varchar, and I decide to run this query to get the totals for each salesperson. 
SELECT SalesPerson
     , AVG(TRY_PARSE(Commission AS int)) AS TotalCommission
 FROM commission
 GROUP BY SalesPerson
GO
What average commission is calculated for Steve?

See possible answers