example of expression access

8/8/2019 Example of Expression Access

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In this article

Introduction

Examples of expressions used in forms and reports

Examples of expressions used in queries and filters

Examples of default value expressions

Examples of field validation rule expressions

Examples of macro condition expressions

Introduction

Often you need information that isn't directly available in a field in your database.

For example, you might need to calculate sales tax on an order. At other times, you

need to supply a query or a filter with criteria information that determines which

records you work with. Perhaps you want to set a default value for a field or control,

or a validation rule for a field or table. In all of these cases, you use an expression.

This article provides examples of expressions. The examples are organized first by

where you would employ them, such as in a form or report, or as a default value.

Then they're organized by what they do, such as manipulate text or calculate

arithmetic values. The examples are designed to work in databases that use the

default ANSI SQL query mode, which is ANSI-89.

In Access, the term expression is synonymous with formula. An expression consists

of a number of possible elements that are used, alone or in combination, to produce

a result. These elements include identifiers (the names of fields, controls, or

properties), operators such as + (plus) or - (minus), functions, constants, and

values. You use an expression to perform a calculation, retrieve the value of a

control, supply criteria to a query, define rules, create calculated controls and

calculated fields, and define a group level for a report.

For more information about how and where to use expressions, see the article

Create an expression.

Examples of expressions used in forms and reports

This section contains examples of expressions that you can use to create a

calculated control in a form or report. A calculated control is a control whose

ControlSource property is an expression, instead of a field. Calculated controls are
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easy to spot, because they always start with the = (equal sign) operator. You use

the ControlSource property to tell Access where to get the data for the control.

To enter an expression in a control (for this example, a text box control)

In the Database window, under Objects, click Forms or Reports.

Click the form or report, and then click Design in the Database window.

Click the text box to select it.

On the View menu, click Properties to display the property sheet for the text box.

Change the value in the Control Source property box of the text box to the

expression. For example, insert an expression from the Expression column in the

table in the following section.

Close the property sheet.

Expressions that combine or manipulate text

The expressions in the following table use the & (ampersand) and the + (plus)

operators to combine text strings, or use built-in functions to operate on a text

string, or otherwise operate on text to create a calculated control.

Expression Result

="N/A" Displays N/A.

=[FirstName] & " " &[LastName]

Displays the values of the FirstName and LastNamefields, separated by a space.

=Left([ProductName], 1) Uses the Left function to display the first character of

the value of the ProductName control.

=Right([AssetCode], 2) Uses the Right function to display the last 2 characters

of the value of the AssetCode control.

=Trim([Address]) Uses the Trim function to display the value of the

Address control, removing any leading or trailing

spaces.

=IIf(IsNull([Region]), [City]

& " " & [PostalCode],

[City] & " " & [Region] & "

" & [PostalCode])

Uses the IIf function to display the values of the City

and PostalCode controls if the value in the Region

control is null; otherwise, it displays the values of the

City, Region, and PostalCode controls, separated by
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spaces.

=[City] & (" " + [Region])

& " " & [PostalCode]

Uses the + operator and null propagation to display the

values of the City and PostalCode controls if Region is

null; otherwise, it displays the values of the City,

Region, and PostalCode controls, separated by spaces.Null propagation means that if any component of an

expression is null, the entire expression is also null.

The + operator supports null propagation; the &

operator does not.

Expressions for headers and footers

You use the Page and the Pages properties to display or print page numbers in

forms or reports. The Page and Pages properties are available only during printing

or print preview, so they are not listed on the property sheet. Most often, you place

expressions such as these in a text box control in the header or footer section ofyour form or report.

Expression Result

=[Page] 1

="Page " & [Page] Page 1

="Page " & [Page] & " of " &

[Pages]

Page 1 of 3

=[Page] & " of " & [Pages] & "

Pages"

1 of 3 Pages

=[Page] & "/" & [Pages] & "

Pages"

1/3 Pages

=[Country] & " - " & [Page] UK - 1

=Format([Page], "000") 001

="Printed on: " & Date() Printed on:

12/31/04

Expressions that perform arithmetic operations

You can use expressions to add, subtract, multiply, and divide the values in two or

more fields or controls. You can also use expressions to perform arithmetic
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operations on dates. For example, if RequiredDate is a Date/Time data type field or

control, the expression =[RequiredDate] - 2 returns a Date/Time value equal to two

days before RequiredDate.

Expression Result

=[Subtotal]+[Freight] The sum of the values of the Subtotal and Freight

controls.

=[RequiredDate]-

[ShippedDate]

The difference between the values of the

RequiredDate and ShippedDate controls.

=[Price]*1.06 The product of the value of the Price control and 1.06

(adds 6 percent to the Price value).

=[Quantity]*[Price] The product of the values of the Quantity and Price

controls.

=[EmployeeTotal]/

[CountryTotal]

The quotient of the values of the EmployeeTotal and

CountryTotal controls.

Note When you use an arithmetic operator (+, -, *, and /) in an expression, and the

value of one of the controls in the expression is null, the result of the entire

expression will be null. If some records in one of the controls that you used in the

expression might have a null value, you can convert the null value to zero by using

the Nz function, for example, =Nz([Subtotal])+Nz([Freight]). See the article Nz

function for more information.

Expressions that refer to values in controls

Sometimes you need a value that exists somewhere else, such as in a field or

control on another form or report. You can use an expression to return the value

from another field or control.

The following table lists examples of expressions that you can use in calculated

controls on forms.

Expression Result

=Forms![Orders]![OrderID] The value of the OrderID control on the Orders

form.

=Forms![Orders]![Orders

Subform].Form![OrderSubtotal]

The value of the OrderSubtotal control on the

Orders subform on the Orders form.
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=Forms![Orders]![Orders

Subform]!

[ProductID].Column(2)

The value of the third column in ProductID, a

multiple-column list box on the Orders subform

on the Orders form. (0 refers to the first column,

1 refers to the second column, and so on.)

=Forms![Orders]![OrdersSubform]![Price] * 1.06

The product of the value of the Price control onthe Orders subform on the Orders form and 1.06

(adds 6 percent to the value of the Price control).

=Parent![OrderID] The value of the OrderID control on the main or

parent form of the current subform.

The following table lists examples of expressions that you can use in calculated

controls on reports.

Expression Result

=Reports![Invoice]![OrderID] The value of the OrderID control on the

Invoice report.

=Reports![Summary]![Summary

Subreport]![SalesTotal]

The value of the SalesTotal control on the

Summary subreport on the Summary report.

=Parent![OrderID] The value of the OrderID control on the main

or parent report of the current subreport.

Expressions that count, sum, and average values by using aggregate functions

Often you need to calculate a sum of the values that are stored in a group of

records. For example, you might want to calculate a group total for the group footer

in a report, or an order subtotal for line items on a form. At other times, you need to

count the number of items rather than to sum them; or you need to calculate the

average value. The expressions in the following table use functions that are

designed to aggregate or summarize data. You will often see these functions (for

example, Sum, Count, and Avg) referred to as aggregate functions.

Expression Description

=Avg([Freight]) Uses the Avg function to display the average of the values

of the Freight control.

=Count([OrderID]) Uses the Count function to display the number of records in

the OrderID control.

=Sum([Sales]) Uses the Sum function to display the sum of the values of


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the Sales control.

=Sum([Quantity]*[Pri

ce])

Uses the Sum function to display the sum of the product of

the values of the Quantity and Price controls.

=[Sales]/Sum([Sales])*100

Displays the percentage of sales, determined by dividing thevalue of the Sales control by the sum of all the values of the

Sales control.

Note If the Format property of the control is set to Percent,

do not include *100 in the expression.

Expressions that selectively count, sum, and look up values by using domain

aggregate functions

Sometimes you need to sum or count values selectively. For example, you might

want to count only those values that are within a certain range or that evaluate toYes. At other times you might need to look up a value from another table for

display. Access supports a series of functions that can be used for this sort of task.

They are called the domain aggregate functions.


=DLookup("[ContactName]", "[Suppliers]",

"[SupplierID] = " & Forms("Suppliers")

("[SupplierID]"))

Uses the DLookup function to return

the value of the ContactName field in

the Suppliers table where the value

of the SupplierID field in the table

matches the value of the SupplierID

control on the Suppliers form.

=DLookup("[ContactName]", "[Suppliers]",

"[SupplierID] = " & Forms![New Suppliers]!

[SupplierID])

Uses the DLookup function to return

the value of the ContactName field in

the Suppliers table where the value

of the SupplierID field in the table

matches the value of the SupplierID

control on the New Suppliers form.

=DSum("[OrderAmount]", "[Orders]","[CustomerID] = 'RATTC'")

Uses the DSum function to return thesum total of the values in the

OrderAmount field in the Orders

table where the CustomerID is

RATTC.

=DCount("[Retired]","[Assets]","[Retired]=Y

es")

Uses the DCount function to return

the number of Yes values in the


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Retired field (a Yes/No field) in the

Assets table.

Expressions that manipulate and calculate dates

Certain things are fundamental to a database application, among them, the need to

track dates and times. You work with dates and times in Access by using the

Date/Time data type. Access can perform arithmetic calculations on dates; for

example, you can calculate how many days have elapsed since the invoice date to

age your accounts receivable. You can format dates and times in numerous ways,

as shown in the following table.


=Date() Uses the Date function to display the current date in the

form of mm-dd-yy, where mm is the month (1 through 12),

dd is the day (1 through 31), and yy is the last two digits ofthe year (1980 through 2099).

=Format(Now(),

"ww")

Uses the Format function to display the week number of the

year for the current date, where ww represents weeks 1

through 53.

=DatePart("yyyy",

[OrderDate])

Uses the DatePart function to display the four-digit year of

the value of the OrderDate control.

=DateAdd("y", -10,

[PromisedDate])

Uses the DateAdd function to display a date that is 10 days

before the value of the PromisedDate control.

=DateDiff("d",

[OrderDate],

[ShippedDate])

Uses the DateDiff function to display the number of days'

difference between the values of the OrderDate and

ShippedDate controls.

=[InvoiceDate] + 30 Uses arithmetic operations on dates to calculate the date 30

days after the date in the InvoiceDate field or control.

Conditional expressions that return one of two possible values

The example expressions in the following table use the IIf function to return one of

two possible values. You pass the IIf function three arguments: The first argument is

an expression that must return a True or False value. The second argument is the

value to return if the expression is true, and the third argument is the value to

return if the expression is false.



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=IIf([Confirmed] = "Yes", "Order

Confirmed", "Order Not

Confirmed")

Uses the IIf function to display the message

"Order Confirmed" if the value of the

Confirmed control is Yes; otherwise, it displays

the message "Order Not Confirmed."

=IIf(IsNull([Country]), " ",

[Country])

Uses the IIf function to display an empty string

if the value of the Country control is null;

otherwise, it displays the value of the Country

control.

=IIf(IsNull([Region]), [City] & " " &

[PostalCode], [City] & " " &

[Region] & " " & [PostalCode])

Uses the IIf function to display the values of the

City and PostalCode controls if the value in the

Region control is null; otherwise, it displays the

values of the City, Region, and PostalCodecontrols.

=IIf(IsNull([RequiredDate]) Or

IsNull([ShippedDate]), "Check for

a missing date", [RequiredDate] -

[ShippedDate])

Uses the IIf function to display the message

"Check for a missing date" if the result of

subtracting ShippedDate from RequiredDate is

null; otherwise, it displays the difference

between the values of the RequiredDate and

ShippedDate controls.

< Back to top >

Examples of expressions used in queries and filters

This section contains examples of expressions that you can use to create a

calculated field in a query or to supply criteria to a query. A calculated field is a

column in a query that results from an expression. For example, you can calculate a

value or format a portion of a date. You use criteria in a query to limit the records

that you work with. For example, you can use the Between operator to supply a

date range for the ShippedDate field in order to limit the query result to orders that

were shipped between those dates.

Expressions that create a calculated field (perform calculations on or manipulate

field values)

The example expressions in the following list can be used to create a calculated

field in a query.

To enter a calculated field in query Design view
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In the Database window, under Objects, click Queries.

Click the query, and then click Design in the Database window.

Click the field cell in the column where you want to create the calculated field.

Type the expression, or click the Build button on the toolbar to create an

expression by using the Expression Builder. You should start the expression with a

name followed by a colon; for example, type ExtendedPrice: to start a calculated

field called ExtendedPrice.

Expressions that manipulate text in a query or filter

The expressions in the following table use the & and the + operators to combine

text strings, use built-in functions to operate on a text string, or otherwise operate

on text to create a calculated field.


FullName: [FirstName] & "

" & [LastName]

Displays the value of the FirstName and LastName

fields, separated by a space, in the FullName field.

Address2: [City] & " " &

[Region] & " " &

[PostalCode]

Displays the value of the City, Region, and PostalCode

fields, separated by spaces, in the Address2 field.

ProductInitial:

Left([ProductName], 1)

Uses the Left function to display, in the ProductInitial

field, the first character of the value in theProductName field.

TypeCode:

Right([AssetCode], 2)

Uses the Right function to display, in the TypeCode

field, the last two characters of the value in the

AssetCode field.

AreaCode:

Mid([Phone],2,3)

Uses the Mid function to display, in the AreaCode field,

the three characters starting with the second

character of the value in the Phone field.

Expressions that perform arithmetic operations in calculated fields

You can use expressions to add, subtract, multiply, and divide the values in two or

more fields or controls. You can also perform arithmetic operations on dates. For

example, if RequiredDate is a Date/Time data type field or control, the expression

=[RequiredDate] - 2 will return a Date/Time value equal to two days before

RequiredDate.


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PrimeFreight: [Freight] * 1.1 Displays freight charges plus 10 percent in the

PrimeFreight field.

OrderAmount: [Quantity] *[UnitPrice]

Displays the product of the values in the Quantityand UnitPrice fields in the OrderAmount field.

LeadTime: [RequiredDate] -

[ShippedDate]

Displays the difference between the values in the

RequiredDate and ShippedDate fields in the

LeadTime field.

TotalStock: [UnitsInStock]+

[UnitsOnOrder]

Displays the sum of the values in the UnitsInStock

and UnitsOnOrder fields in the TotalStock field.

FreightPercentage:

Sum([Freight])/Sum([Subtotal

]) *100

Displays, in the FreightPercentage field, the

percentage of freight charges in each subtotal, by

dividing the sum of the values in the Freight field by

the sum of the values in the Subtotal field. (This

example uses the Sum function.)

The Total row in the design grid must be displayed,

and the Total cell for this field must be set to

Expression.

If the Format property of the field is set to Percent,

do not include *100.

Expressions that manipulate and calculate with dates in calculated fields

Certain things are fundamental to a database application, among them, the need to

track dates and times. You work with dates and times in Access by using the

Date/Time data type. Access can perform arithmetic calculations on dates; for

example, you can calculate how many days have elapsed since the invoice date to

age your accounts receivable. As the following table shows, you can format dates

and times numerous ways.


LagTime: DateDiff("d",

[OrderDate], [ShippedDate])

Uses the DateDiff function to display in the

LagTime field the number of days between the

order date and ship date.


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YearHired: DatePart("yyyy",

[HireDate])

Uses the DatePart function to display in the

YearHired field the year each employee was hired.

MinusThirty: Date( )- 30 Uses the Date function to display the date 30 days

prior to the current date.

Expressions that count, sum, and average values by using SQL aggregate or domain

aggregate functions

Often you need to calculate a sum of the values that are stored in a group of

records. For example, you might need to calculate a group total for the group footer

in a report, or an order subtotal for line items on a form. At other times, you need to

count the number of items rather than to sum them, or you want to calculate the

average value. The expressions in the following table use functions that are

designed to aggregate or summarize data. You will often see these functions (for

example, Sum, Count, and Avg) referred to as aggregate functions.


want to count only those values that are within a certain range, or those that

evaluate to Yes. At other times, you need to look up a value from another table so

that you can display it. Access supports a series of functions that can be used for

this sort of task. These functions are called the domain aggregate functions (for

example, DSum, DCount, and DAvg).

To calculate totals, you will often need to create a totals query. For example, to

summarize by group, you need to use a totals query. To enable a totals query from

the query design grid, click Totals on the View menu.


RowCount:Count(*) Uses the Count function to count the number of

records in the query, including records with null

(blank) fields.

FreightPercentage:

Sum([Freight])/Sum([Subtotal

]) *100

Displays, in the FreightPercentage field, the

percentage of freight charges in each subtotal by

dividing the sum of the values in the Freight field by

the sum of the values in the Subtotal field. (This

example uses the Sum function.)

The Total row in the design grid must be displayed,

and the Total cell for this field must be set to

Expression.

If the Format property of the field is set to Percent,
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do not include *100.

AverageFreight:

DAvg("[Freight]", "[Orders]")

Uses the DAvg function to display, in the

AverageDiscount field, the average discount given

on all orders combined in a totals query.

Expressions for working with fields with missing information (fields with null values)

The expressions shown here work with fields with potentially missing information

those that might have a null value. A null value represents the absence of

information; it does not represent zero, or any value at all. Access supports this idea

of missing information because the concept is vital to the integrity of a database. In

the real world, information is often missing, even if only temporarily (for example,

the as-yet undetermined price for a new product). Therefore, a database that

models a real world entity, such as a business, must be able to record information

as missing. You can use the IsNull function to determine if a field or control contains

a null value, and you can use the Nz function to convert a null value to zero.


CurrentCountry:

IIf(IsNull([Country]), " ", [Country])

Uses the IIf and IsNull functions to display an

empty string in the CurrentCountry field if the

Country field is null; otherwise, it displays the

contents of the Country field.

LeadTime:

IIf(IsNull([RequiredDate] -

[ShippedDate]), "Check for a

missing date", [RequiredDate] -

[ShippedDate])

Uses the IIf and IsNull functions to display, in

the LeadTime field, the message "Check for a

missing date" if the value of either the

RequiredDate field or the ShippedDate field is

null; otherwise, it displays the difference.

SixMonthSales: Nz([Qtr1Sales]) +

Nz([Qtr2Sales])

Displays, in the SixMonthSales field, the total of

the values in the first-quarter and second-

quarter sales fields combined, by first using the

Nz function to convert the null values to zero.

Expression that uses a subquery to create a calculated field

Sometimes a nested query, also called a subquery, can be used to create a

calculated field. A subquery is expressed by using Structured Query Language

(SQL) the query language that Access uses. The expression in the following table

is one example of a calculated field that results from a subquery.

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Cat: (SELECT [CategoryName] FROM [Categories]

WHERE [Products].[CategoryID]=[Categories].

[CategoryID])

Displays the CategoryName, if

the CategoryID from the

Categories table is the same as

the CategoryID from the

Products table.

Expressions used as matching criteria to limit the records you work with

You can use an expression to define the criteria for matching rows in a query.

Access then returns only those rows that match the criteria. In the list that follows,

you will find sample expressions that you can use to define criteria. To define

criteria, you open a query and then click Design, which opens the query design grid.

Then you locate the field for which you want to enter the criteria. Each column in

the query design grid represents a field. Finally, you click in the Criteria cell for that

field and type your criteria.

To enter criteria in the query design grid

In the Database window, under Objects, click Queries.

Click the query, and then click Design in the Database window.

Click in the criteria cell in the column for which you want to enter matching criteria.

Type the criteria expression or click the Build button on the toolbar to create an

expression by using the Expression Builder.

Note Do not precede the criteria expression with the = operator.

If you want a larger area in which to type an expression, press SHIFT+F2 to display

the Zoom box.

Expressions that match whole or partial text values

The sample expressions in the Expression column of the following table define the

criteria that match whole or partial text values.

Field Expression Description

ShipCity "London" Displays orders shipped to London.

ShipCity "London" Or "Hedge

End"

Uses the Or operator to display orders shipped

to London or Hedge End.

ShipCountry In("Canada", "UK") Uses the In operator to display orders shipped

to Canada or the UK.


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ShipCountry Not "USA" Uses the Not operator to display orders

shipped to countries other than the USA.

ProductNam

e

Not Like "C*" Uses the Not operator and the * wildcard

character to display products whose names do

not begin with C.

CompanyNa

me

>="N" Displays orders shipped to companies whose

names start with the letters N through Z.

ProductCode Right([ProductCode],

2)="99"

Uses the Right function to display orders with

ProductCode values that end in 99.

ShipName Like "S*" Displays orders shipped to customers whose

names start with the letter S.

Expressions that use dates in matching criteria

Access can perform arithmetic calculations on dates; for example, you can use the

OrderDate field to display orders more than 30 days old (see the following table).

You can also use a variety of built-in functions to extract and manipulate portions of

dates or to place a date within calendar periods (for example, to determine what

calendar quarter a date is in). The sample expressions that follow demonstrate the

use of dates and related functions in criteria expressions.


ShippedDa

te

#2/2/2000# Displays orders shipped on

February 2, 2000.

ShippedDa

te

Date() Displays orders shipped today.

RequiredD

ate

Between Date( ) And DateAdd("m",

3, Date( ))

Uses the Between...And operator

and the DateAdd and Date

functions to display orders

required between today's date

and three months from today'sdate.

OrderDate < Date( ) - 30 Uses the Date function to display

orders more than 30 days old.

OrderDate Year([OrderDate])=2005 Uses the Year function to display


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orders with order dates in 2005.

OrderDate DatePart("q", [OrderDate])=4 Uses the DatePart function to

display orders for the fourth

calendar quarter.

OrderDate DateSerial(Year ([OrderDate]),

Month([OrderDate])+1, 1)-1

Uses the DateSerial, Year, and

Month functions to display orders

for the last day of each month.

OrderDate Year([OrderDate])= Year(Now())

And Month([OrderDate])=

Month(Now())

Uses the Year and Month

functions and the And operator to

display orders for the current year

and month.

ShippedDa

te

Between #1/5/2005# And

#1/10/2005#


to display orders shipped no

earlier than 5-Jan-2005 and no

later than 10-Jan-2005.

RequiredD

ate

Between Date( ) And DateAdd("M",

3, Date( ))


to display orders required

between today's date and three

months from today's date.

BirthDate Month([BirthDate])=Month(Date()) Uses the Month and Date

functions to display employeeswho have birthdays this month.

Expressions that match a missing value (null) or a zero-length string

The expressions in the following table work with fields that have potentially missing

information those that might contain a null value or a zero-length string. A null

value represents the absence of information; it does not represent a zero or any

value at all. Access supports this idea of missing information because the concept is

vital to the integrity of a database. In the real world, information is often missing,

even if only temporarily (for example, the as-yet undetermined price for a new

product). Therefore, a database that models a real world entity, such as a business,must be able to record information as missing. You can use the IsNull function to

determine if a field or control contains a null value, and you can use the Nz function

to convert a null value to zero.

Field

Expressio

n Description


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ShipRegi

on

Is Null Displays orders for customers whose ShipRegion field is null

(missing).

ShipRegi

on

Is Not Null Displays orders for customers whose ShipRegion field

contains a value.

Fax "" Displays orders for customers who don't have a fax machine,

indicated by a zero-length string value in the Fax field instead

of a null (missing) value.

Expressions that use patterns to match records

The Like operator provides a great deal of flexibility when you are trying to match

rows that follow a pattern. That is because Like can be used with special characters

called wildcard characters that let you define patterns for Access to match. For

example, the * (asterisk) wildcard character matches a sequence of characters of

any type, and makes it easy to find all names that begin with a letter. You use theexpression Like "S*" to find all names that begin with the letter S, for example. For

more information, see the article Like operator.


ShipNa

me

Like "S*" Orders shipped to customers whose names start with

the letter S.

ShipNa

me

Like "*Imports"

Orders shipped to

customers

Orders shipped to customers whose names end with

the word "Imports".

ShipNa

me

Like "[A-D]*" Orders shipped to customers whose names start with

A through D.

ShipNa

me

Like "*ar*" Orders shipped to customers whose names include

the letter sequence "ar".

ShipNa

me

Like "Maison

Dewe?"

Orders shipped to the customer with "Maison" as the

first part of its name and a five-letter second name in

which the first four letters are "Dewe" and the lastletter is unknown.

ShipNa

me

Not Like "A*" Orders shipped to customers whose names do not

start with the letter A.

Expressions that match rows based on the result of a domain aggregate function
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want to count only those values that are within a certain range, or that evaluate to

Yes. At other times you might need to look up a value from another table so that

you can display it. Access supports a series of functions called the domain

aggregate functions (for example, DSum, DCount, and DAvg) that can be used for

this sort of task. The sample expressions in the following table use the domainaggregate functions to perform a calculation on a set of values, and use the result

as the query criteria.


Freight > (DStDev("[Freight]",

"Orders") +

DAvg("[Freight]", "Orders"))

Uses the DAvg and DStDev functions to

display all orders for which the freight cost

rose above the mean plus the standard

deviation for freight cost.

Quantit

y

> DAvg("[Quantity]",

"[Order Details]")

Uses the DAvg function to display products

ordered in quantities above the average

order quantity.

Expressions that match based on the results of subqueries

Sometimes a nested query, also called a subquery, can be used to calculate a value

to be used as the criteria. A subquery is expressed by using Structured Query

Language (SQL) the query language that Access uses. The sample expressions in

the following table match rows based on the results from a subquery.

Field Expression Displays

UnitPrice (SELECT [UnitPrice] FROM

[Products] WHERE

[ProductName] = "Aniseed

Syrup")

Products whose price is the same

as the price of Aniseed Syrup.

UnitPrice >(SELECT AVG([UnitPrice])

FROM [Products])

Products that have a unit price

above the average.

Salary > ALL (SELECT [Salary] FROM[Employees] WHERE ([Title] LIKE

"*Manager*") OR ([Title] LIKE

"*Vice President*"))

Salary of every salesrepresentative whose salary is

higher than that of all employees

with "Manager" or "Vice President"

in their titles.

OrderTotal:

[UnitPrice] *

> (SELECT AVG([UnitPrice] *

[Quantity]) FROM [Order

Orders with totals that are higher


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[Quantity] Details]) than the average order value.

Expressions used to update the data in an update query

Often you need to modify the values in a column in your database. One of the ways

that you can do this is by using an update query. With an update query, you can tell

Access which records to update and how to compute the new values for the fields

that you want to update. When you create an update query to update a field, you

provide the expression that supplies the replacement value. The expressions in the

following table represent example expressions that supply a replacement value.

Use expressions such as the following in the Update To cell in the query design grid

for the field that you want to update.

Field Expression Result

Title "Salesperson" Changes a text value to Salesperson.

ProjectStart #8/10/99# Changes a date value to 10-Aug-99.

Retired Yes Changes a No value in a Yes/No field to Yes.

PartNumber "PN" & [PartNumber] Adds PN to the beginning of each specified

part number.

LineItemTot

al

[UnitPrice] * [Quantity] Calculates the product of UnitPrice and

Quantity.

Freight [Freight] * 1.5 Increases freight charges by 50 percent.

Sales DSum("[Quantity] *

[UnitPrice]",

"Order Details",

"[ProductID]=" &

[ProductID])

Where the ProductID values in the current

table match the ProductID values in the Order

Details table, updates sales totals based on

the product of Quantity and UnitPrice.

ShipPostalC

ode

Right([ShipPostalCode],

5)

Truncates the leftmost characters, leaving the

five rightmost characters.

UnitPrice Nz([UnitPrice]) Changes a null (Null: A value you can enter in

a field or use in expressions or queries to

indicate missing or unknown data. In Visual

Basic, the Null keyword indicates a Null value.

Some fields, such as primary key fields, can't

contain Null.) value to a zero (0) in the
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UnitPrice field.

Expressions used in SQL statements

Structured Query Language, or SQL, is the query language that Access uses. Every

query that you create in query Design view can also be expressed by using SQL. To

see the SQL for any query, click SQL View on the View menu. The following table

shows sample SQL statements that employ an expression.

SQL statement that uses an expression Result

SELECT [FirstName],[LastName] FROM

[Employees] WHERE

[LastName]="Davolio"

Displays the values in the FirstName and

LastName fields for employees whose last

name is Davolio.

SELECT [ProductID],[ProductName]

FROM [Products] WHERE[CategoryID]=Forms![New Products]!

[CategoryID];

Displays the values in the ProductID and

ProductName fields in the Products table forrecords in which the CategoryID value

matches the CategoryID value specified in

an open New Products form.

SELECT Avg([ExtendedPrice]) AS

[Average Extended Price] FROM [Order

Details Extended] WHERE

[ExtendedPrice]>1000;

Calculates the average extended price for

orders for which the value in the

ExtendedPrice field is more than 1000, and

displays it in a field named Average

Extended Price.

SELECT [CategoryID],

Count([ProductID]) AS

[CountOfProductID] FROM [Products]

GROUP BY [CategoryID] HAVING

Count([ProductID])>10;

In a field named CountOfProductID, displays

the total number of products for categories

with more than 10 products.

< Back to top >

Examples of default value expressions

It is often useful to give a field or control a default value. That way, Access suppliesthe default value when a new record with the field is created or when the object

that contains the control is created. The expressions in the following table represent

the sample default values for a field or control.

To enter a default value for a field in a table

In the Database window, under Objects, click Tables.
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Click the table, and then click Design in the Database window.

Click the field name for the field that you want.

Click the Default Value property box.

Type the expression, or click the Build button to the right of the property box to

create an expression by using the Expression Builder.

If a control is bound to a field in a table, and the field has a default value, the

default value of the control takes precedence.

Field Expression Default field value

Quantity 1 1

Region "MT" MT

Region "New York,

N.Y."

New York, N.Y. (Note that you must enclose the value in

quotation marks if it includes punctuation.)

Fax "" A zero-length string to indicate that by default this field

should be empty instead of a null value

Order

Date

Date( ) Today's date

DueDate Date() + 60 The date 60 days forward from today

< Back to top >

Examples of field validation rule expressions

You can create a validation rule for a field or control by using an expression. Access

then enforces the rule when data is entered into the field or control. To create a

validation rule, you modify the ValidationRule property of the field or control. You

should also consider setting the ValidationText property, which holds the text that

Access displays when the validation rule is violated. If you don't set the

ValidationText property, Access displays a default error message.

The examples in the following table demonstrate the validation rule expressions for

the ValidationRule property and the associated text for the ValidationText property.

To enter a validation rule for a field in a table

In the Database window, under Objects, click Tables.
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Click the table, and then click Design in the Database window.

Click the field name for the field that you want.

Click the Validation Rule property box.

Type the expression, or click the Build button to the right of the property box to

create an expression by using the Expression Builder.

Note Do not precede the expression with the = operator when you create a

validation rule.

ValidationRule property ValidationText property

0 Please enter a nonzero value.

0 Or > 100 Value must be either 0 or more than 100.

Like "K???" Value must be four characters beginning with

the letter K.

< #1/1/2005# Enter a date prior to 1/1/2005.

>= #1/1/2005# And

Examples of macro condition expressions

In some cases, you might want to carry out an action or series of actions in a macro

only if a particular condition is true. For example, suppose you want an action to run

only when the value of the Counter text box is 10. You use an expression to define

the condition in the Condition column of the macro: [Counter]=10.

To enter a condition for a macro action

In the Database window, under Objects, click Macros.

Click the macro, and then click Design in the Database window.

Click the Condition cell for the macro action.

If the Condition column is not visible, on the View menu, click Conditions.

Type a conditional expression.
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Close the macro.

As with the ValidationRule property, the Condition column expression is a

conditional expression. It must resolve to either a True or False value. The action

takes place only when the condition is true.

Use this expression To carry out the action if

[City]="Paris" Paris is the City value in the field on the form

from which the macro was run.

DCount("[OrderID]", "Orders") > 35 There are more than 35 entries in the OrderID

field of the Orders table.

DCount("*", "[Order Details]",

"[OrderID]=" & Forms![Orders]!

[OrderID]) > 3

There are more than three entries in the Order

Details table for which the OrderID field of the

table matches the OrderID field on the Ordersform.

[ShippedDate] Between #2-Feb-

2005# And #2-Mar-2005#

The value of the ShippedDate field on the form

from which the macro is run is no earlier than

2-Feb-1995 and no later than 2-Mar-1995.

Forms![Products]![UnitsInStock] < 5 The value of the UnitsInStock field on the

Products form is less than 5.

IsNull([FirstName]) The FirstName value on the form from which

the macro is run is null (has no value). This

expression is equivalent to [FirstName] Is null.

[Country]="UK" And Forms!

[SalesTotals]![TotalOrds] > 100

The value in the Country field on the form from

which the macro is run is UK, and the value of

the TotalOrds field on the SalesTotals form is

greater than 100.

[Country] In ("France", "Italy",

"Spain") And Len([PostalCode])5

The value in the Country field on the form from

which the macro is run is either France, Italy,

or Spain, and the postal code is not 5characters long.

MsgBox("Confirm changes?",1)=1 You click OK in a dialog box that the MsgBox

function displays. If you click Cancel in the

dialog box, Access ignores the action.


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Note To force Access to temporarily ignore an action, enter False as a condition.

Forcing Access to temporarily ignore an action can be helpful when you are trying to

find problems in a macro

example of expression access

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