# question

## Automatic calculation problem

I have two tables called TimeCardHours and Employee. Below are the structure of those. create table TimeCardsHours ( TimeCardDetailID int identity (1,1) constraint pkTimeCardDetailID primary key, TimeCardID char (10), DateWorked datetime not null , ProjectID char (10), WorkDescription varchar (100), BillableHours int constraint chkBillableHours check (BillableHours>0), TotalCode int, WorldCodeID char (10) ) create table Employee ( EmployeeID int identity (1,1) constraint pkemployeeid primary key, FirstName char (10) not null, LastName char(10), Title char (10) constraint chktitle check (title in ('Trainee','Team Member','Team Leader','Project Manager','Senior Project Manager')), Phone char (20) not null constraint chkemployeephone check (phone like ('([0-9],[0-9],[0-9])-([0-9],[0-9],[0-9])-([0-9],[0-9],[0-9],[0-9])')), BillingRate int constraint chkbillingrate check (billingrate>0) ) Now I have a question like below: The total cost in TimeCardHourse should be automatically calculated using the formula (Billable hours * Billing rate for the employee to whom the time card is issued.) I gave a big try to do this, but I failed. please help me..Please..

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you can create a view for this select , total_cost = t.BillableHours * e.BillingRate from TimeCardsHours t inner join Employee e on t.EmployeeID = e.EmployeeID

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What if the billing rate for an employee changes?
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that is for sepala to answer. It really depends on what is the business rule
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OK. [Computed Column][1] doesn't appear to do what you need (a sub-query). Other options: 1. [Trigger][2]. When details are inserted / updated into the TimeCardHours, the trigger calculates the TotalCost value 2. Control access using a [stored procedure][3], and have that calculate the TotalCost. I would probably go for the Trigger in this situation, just to ensure that the calculations are performed as they should be during normal operations (assuming normal operations doesn't include bulk loading this table). You should also consider putting a "billed" field on the TimeCardHours table, so that the trigger knows not to update the costs on that one... [1]: http://msdn.microsoft.com/en-us/library/ms191250.aspx [2]: http://msdn.microsoft.com/en-us/library/ms189799.aspx [3]: http://msdn.microsoft.com/en-us/library/ms187926.aspx
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@Grant - thanks for the Thumbs-Up! That pushed me over 1k rep...
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I would suggest moving the BillingRate into a separate table with ValidFrom and ValidTo to cover the possibility of a changing BillingRate. I prefer the view to a trigger/sproc, as a calculated value like this can change so often. Another possibility is storing the billing rate in the TimCardsHours table directly with the BillableHours and then creating a computed column for that. CREATE TABLE TimeCardsHours (TimeCardDetailID int IDENTITY(1, 1) CONSTRAINT pkTimeCardDetailID PRIMARY KEY, TimeCardID char(10), DateWorked datetime NOT NULL, ProjectID char(10), WorkDescription varchar(100), BillableHours int CONSTRAINT chkBillableHours CHECK (BillableHours > 0), BillingRate int CONSTRAINT chkbillingrate CHECK (billingrate > 0), TotalCost AS (BillableHours * BillingRate), TotalCode int, WorldCodeID char(10)) CREATE TABLE Employee (EmployeeID int IDENTITY(1, 1) CONSTRAINT pkemployeeid PRIMARY KEY, FirstName char(10) NOT NULL, LastName char(10), Title char(10) CONSTRAINT chktitle CHECK (title IN ('Trainee', 'Team Member', 'Team Leader', 'Project Manager', 'Senior Project Manager')), Phone char(20) NOT NULL CONSTRAINT chkemployeephone CHECK (phone LIKE ('([0-9],[0-9],[0-9])-([0-9],[0-9],[0-9])-([0-9],[0-9],[0-9],[0-9])'))) SELECT * FROM TimeCardsHours t INNER JOIN Employee e ON t.EmployeeID = e.EmployeeID
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That's why I like these questions - you get several different options to think about, and it shows how different approaches can be used. All in, this place is a great place to learn!
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As an evil way to do this, you *could* put the calculation in a user defined function and call that as part of your computed column. However, this would be entirely evil when used in a large data scenario. Functions are bad enough for performance, let alone ones which do data lookups. But, it is an option. /* * Scalar Function: fn_ExampleScalarLookupFunction * Created By: Matthew.Whitfield */ CREATE FUNCTION [dbo].[fn_ExampleScalarLookupFunction ](@value int) RETURNS int AS BEGIN RETURN (SELECT SUM([TestColumn2]) FROM test2 WHERE [TestColumn] = @value) END

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Too true RE evil! Beelzebub would be proud ;-)
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(Irrelevant mental meandering - I now have Queen's Bohemian Rhapsody in my head. And I've got a three hour drive to get home, with no CD / MP3 player. I'll just have to see what the BBC can offer up...)
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Thomas, so it'll be a pretty "Wayne's Worldy" drive for you...
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:-) A certain amount of headbangery - the music sampled ranged from a Mozart string quartet through to some popular young musicians scouting for girls. Or something. I'm getting old, you know... (BBC Radios 3 & 2. Got home before I needed to switch to BBC Radio 4 for "The Now Show")
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