15-dot-3-Advanced-Expressions.md
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We can use arithmetic to get a percentage of one value compared to an aggregate value.
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**The following expression determines the percentage of an order’s cost paid for shipping:**
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-```
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-([Orders].[Freight])/(([Order Details].[UnitPrice]) * ([Order Details].[Quantity])+([Orders].[Freight]))
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-```
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+``([Orders].[Freight])/(([Order Details].[UnitPrice]) * ([Order Details].[Quantity])+([Orders].[Freight]))``
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![expressions5](http://wiki.izenda.us/FAQ/FAQ/expressions5.png)
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If we break the total equation into steps, the problem becomes clearer:
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-1): Calculate UnitPrice*Quantity for each ProductID within an OrderID.
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-2): Sum these calculated values into a hypothetical TotalUnitPrice for the OrderID.
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-3): Add Freight to TotalUnitPrice and divide Freight by this value to get a percentage freight cost of total order cost.
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+1. Calculate UnitPrice*Quantity for each ProductID within an OrderID.
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+2. Sum these calculated values into a hypothetical TotalUnitPrice for the OrderID.
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+3. Add Freight to TotalUnitPrice and divide Freight by this value to get a percentage freight cost of total order cost.
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Since expressions cannot create fields, but only display calculations based on fields, expressions cannot execute step 2. Steps 1 and 2 should be calculated in a view, which would create a computed column that can be used in an expression for step 3.
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