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06 – Expression Builder

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Session Aims & Objectives• Aims

– To use expressions to perform more complex calculations in forms

• Objectives,by end of this week’s sessions, you should be able to:

– create an expression that calculates a value using existing table fields

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What is an Expression…• A set of Data and Operators

• Used to select data in a query– "PT0010" Or "PT0011" Or "PT0012"

• Used to calculate a value– [Unit Price]*[Quantity]

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When do we use them…

• In queries– Select records with multiple values– Select records on a calculated value

•[Order Date] = Now()•Sum([Unit Price]*[Quantity]) >= 100

• In Reports or Form– Calculate values that are not stored

• Order Price = Sum([Unit Price]*[Quantity])

• VAT = Order Price*0.175

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Why use Expressions…• Only store values that cannot be calculated from

others– Wish to use these values– Use additional values for Reports

• Group Summary• Report Summary

• Allows more flexibility when asking ‘questions’– Specify more values in a query– Find range

• Less than• Greater than• etc.

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Expression Builder…• Let Access do the hard work

• Built in Expression Builder– Allow easy selection of values– Combination with operators

• Simple +, -, *, /• More complex Sum, LIKE, And, Or, Not

Icon

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Expression Builder…

Expression

Basic Operators

Objects

Fields/Groups

Values/Operators

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Expression Builder…

‘Object’ currently in

‘Objects’in Database

General Function

Constant Values

Basic Operators(AND, OR, NOT, MOD<=, =)

Commonly used Expression(Page N of M, Date/Time)

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Building Expressions…• Select vales from the windows

– Use ‘Current Object’ for values on the query/form etc being worked on

– When using multiple objects• Select type from first window• ‘Loaded’ from the expanded list• ‘Values’ from other windows

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Uses for Expressions…• Calculate a value in a

form– Sum of all the order

lines– Sum of an order– VAT– Grand Total

• Selecting records from a Query– When stock falls below

a certain level– All orders placed in the

last month

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An Example…• Customer Order Form

– Similar to the Order details form from last lecture

– Views cost of order as well

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An Example…• Build the Order Details Main and Sub Order

Form from lecture 5– Include the cost information as well

• Products - Unit Price

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New Sub Form Query…

• Main form query same as last weeks lecture

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New Sub Form…

• Need to add line price– Extend form (left)– Add new Text Box (Details) and Label (Header)

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Calculating Totals…

• Text box is Unbound– Open Properties– Set Name– Select Control Source– Click …

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Calculating Totals…• Expression Builder will

launch

– Must multiple [Quantity] and [Unit Price]

– Select values from the relevant list object

– Use buttons for simple operators

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Calculating Totals…

– Expression now displayed in the Control Source of the text box

– Also in text of box

• Need to calculate total for all lines– This value will be

stored in the footer

– Extend footer and add text box and label

– Rename– Set control source to

Sum the Total values• =Sum([Quantity][Unit Price])

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Final Sub Form…

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Creating Main Form…• Use same query as last weeks lecture

– Create column form– Move fields– Add header– Insert new sub form– Link

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Creating Main Form…

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Main Form Totals…• Need to add totals to

main form– Sub Total– VAT– Grand Total

• Add 3 text boxes and labels to footer– Format as desired– Set Names and

Captions as needed

• Sub Total– Already calculated on

Sub Form footer

• VAT– =[SubTotal]*0.175

• Grand Total– =[SubTotal]+VAT]

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Main Form Totals…• Sub Total Box

– Set control Source equal to OrderTotal on sub form

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Sub Total Expressions…

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VAT…

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Grand Total…

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Final Design…

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Final Form…

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Tutorial Exercise: Countries• Task 1: Use a form and sub-form to enter

data for Countries and Continents

• Task 2: Create a query that includes calculated fields for population density and population change