Examples of expressions
This article provides many examples of expressions in Access. An expression is a combination of mathematical or logical operators, constants, functions, table fields, controls, and properties that evaluates to a single value. You can use expressions in Access to calculate values, validate data, and set a default value.
In this article
Forms and reports
Queries and filters
Tables
Macros
Forms and reports
The tables in this section provide examples of expressions that calculate a value in a control located on a form or report. To create a calculated control, you enter an expression in the ControlSource property of the control, instead of in a table field or query.
Note You can also use expressions in a form or report when you Highlight data with conditional formatting.
Text operations
The expressions in the following table use the & (ampersand) and the + (plus) operators to combine text strings, built-in functions to manipulate 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 that reside in table fields called FirstName and LastName. In this example, the & operator is used to combine the FirstName field, a space character (enclosed in quotation marks), and the LastName field. |
| =Left([ProductName], 1) | Uses the Left function to display the first character of the value of a field or control called ProductName. |
| =Right([AssetCode], 2) | Uses the Right function to display the last 2 characters of the value in a field or control called AssetCode. |
| =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 spaces. |
| =[City] & (" " + [Region]) & " " & [PostalCode] | Uses the + operator and null propagation to display the values of the City and PostalCode controls if the value in the Region field or control is null; otherwise, it displays the values of the City, Region, and PostalCode fields or 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. |
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 do not appear on the property sheet for the form or report. Typically, you use these properties by placing a text box in the header or footer section of the form or report, and then using an expression, such as the ones shown in the following table.
For more information about using headers and footers in forms and reports, see the article Insert page numbers into a 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/region] & " - " & [Page] | UK - 1 |
| =Format([Page], "000") | 001 |
| ="Printed on: " & Date() | Printed on: 12/31/17 |
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 operations on dates. For example, suppose you have a Date/Time table field named RequiredDate. In the field, or in a control bound to the field, the expression =[RequiredDate] - 2 returns a date/time value equal to two days before the current values in the RequiredDate field.
| Expression | Result |
|---|---|
| =[Subtotal]+[Freight] | The sum of the values of the Subtotal and Freight fields or controls. |
| =[RequiredDate]-[ShippedDate] | The interval between the date values of the RequiredDate and ShippedDate fields or controls. |
| =[Price]*1.06 | The product of the value of the Price field or control and 1.06 (adds 6 percent to the Price value). |
| =[Quantity]*[Price] | The product of the values of the Quantity and Price fields or controls. |
| =[EmployeeTotal]/[CountryRegionTotal] | The quotient of the values of the EmployeeTotal and CountryRegionTotal fields or 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 — this is known as Null propagation. If any records in one of the controls that you use in the expression might have a null value, you can avoid Null propagation by converting the null value to zero by using the Nz function — for example, =Nz([Subtotal])+Nz([Freight]).
Values in other 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 subform named Orders Subform on the Orders form. |
| =Forms![Orders]![Orders Subform]![ProductID].Column(2) | The value of the third column in ProductID, a multiple-column list box on the subform named Orders Subform on the Orders form. (Note that 0 refers to the first column, 1 refers to the second column, and so on.) |
| =Forms![Orders]![Orders Subform]![Price] * 1.06 | The product of the value of the Price control on the subform named 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 expressions in the following table show some ways to use calculated controls on reports. The expressions reference the Report Property.
| Expression | Result |
|---|---|
| =Report![Invoice]![OrderID] | The value of a control called "OrderID" in a report called "Invoice." |
| =Report![Summary]![Summary Subreport]![SalesTotal] | The value of the SalesTotal control on the subreport named Summary Subreport on the Summary report. |
| =Parent![OrderID] | The value of the OrderID control on the main or parent report of the current subreport. |
Count, sum, and average values
You can use a type of function called an aggregate function to calculate values for one or more fields or controls. For example, you can calculate a group total for the group footer in a report, or an order subtotal for line items on a form. You can also count the number of items in one or more fields or calculate an average value.
The expressions in the following table show some of the ways to use functions such as Avg, Count, and Sum.
| Expression | Description |
|---|---|
| =Avg([Freight]) | Uses the Avg function to display the average of the values of a table field or control named "Freight." |
| =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 the Sales control. |
| =Sum([Quantity]*[Price]) | Uses the Sum function to display the sum of the product of the values of the Quantity and the Price controls. |
| =[Sales]/Sum([Sales])*100 | Displays the percentage of sales, determined by dividing the value of the Sales control by the sum of all the values of the Sales control. If you set the Format property of the control to Percent, do not include *100 in the expression. |
For more information about using aggregate functions and totaling the values in field and columns, see the articles Sum data by using a query, Count data by using a query, Display column totals in a datasheet using a Totals row, and Display column totals in a datasheet.
SQL aggregate functions
You use a type of function called an SQL or domain aggregate function when you need to sum or count values selectively. A "domain" consists of one or more fields in one or more tables, or one or more controls on one or more forms or reports. For example, you can match the values in a table field with the values in a control on a form.
| Expression | Description |
|---|---|
| =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 the sum total of the values in the OrderAmount field in the Orders table where the CustomerID is RATTC. |
| =DCount("[Retired]","[Assets]","[Retired]=Yes") | Uses the DCount function to return the number of Yes values in the Retired field (a Yes/No field) in the Assets table. |
Date operations
Tracking dates and times is a fundamental database activity. 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.
| Expression | Description |
| =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 of the 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. |
Conditions of only two 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.
| Expression | Description |
|---|---|
| =IIf([Confirmed] = "Yes", "Order Confirmed", "Order Not Confirmed") | Uses the IIf (Immediate If) 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/region]), " ", [Country]) | Uses the IIf and IsNull functions to display an empty string if the value of the Country/region control is null; otherwise, it displays the value of the Country/region control. |
| =IIf(IsNull([Region]), [City] & " " & [PostalCode], [City] & " " & [Region] & " " & [PostalCode]) | Uses the IIf and IsNull functions 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 fields or controls. |
| =IIf(IsNull([RequiredDate]) Or IsNull([ShippedDate]), "Check for a missing date", [RequiredDate] - [ShippedDate]) | Uses the IIf and IsNull functions to display the message "Check for a missing date" if the result of subtracting ShippedDate from RequiredDate is null; otherwise, it displays the interval between the date values of the RequiredDate and ShippedDate controls. |
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, combine text values such as first and last names, 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 starting and ending date and limit the results of your query to orders that were shipped between those dates.
The following provide examples of expressions for use in queries.
Text operations
The expressions in the following table use the & and + 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.
| Expression | Description |
|---|---|
| FullName: [FirstName] & " " & [LastName] | Creates a field called FullName that displays the values in the FirstName and LastName fields, separated by a space. |
| Address2: [City] & " " & [Region] & " " & [PostalCode] | Creates a field called Address2 that displays the values in the City, Region, and PostalCode fields, separated by spaces. |
| ProductInitial: Left([ProductName], 1) | Creates a field called ProductInitial, and then uses the Left function to display, in the ProductInitial field, the first character of the value in the ProductName field. |
| TypeCode: Right([AssetCode], 2) | Creates a field called TypeCode, and then uses the Right function to display the last two characters of the values in the AssetCode field. |
| AreaCode: Mid([Phone],2,3) | Creates a field called AreaCode, and then uses the Mid function to display the three characters starting with the second character of the value in the Phone field. |
| ExtendedPrice: CCur([Order Details].[Unit Price]*[Quantity]*(1-[Discount])/100)*100 | Names the calculated field ExtendedPrice, and uses the CCur function to calculate the line item totals with an applied discount. |
Arithmetic operations
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, suppose you have a Date/Time field called RequiredDate. The expression =[RequiredDate] - 2 returns a Date/Time value equal to two days before the value in the RequiredDate field.
| Expression | Description |
|---|---|
| PrimeFreight: [Freight] * 1.1 | Creates a field called PrimeFreight, and then displays freight charges plus 10 percent in the field. |
| OrderAmount: [Quantity] * [UnitPrice] | Creates a field called OrderAmount, and then displays the product of the values in the Quantity and UnitPrice fields. |
| LeadTime: [RequiredDate] - [ShippedDate] | Creates a field called LeadTime, and then displays the difference between the values in the RequiredDate and ShippedDate fields. |
| TotalStock: [UnitsInStock]+[UnitsOnOrder] | Creates a field called TotalStock, and then displays the sum of the values in the UnitsInStock and UnitsOnOrder fields. |
| FreightPercentage: Sum([Freight])/Sum([Subtotal]) *100 | Creates a field called FreightPercentage, and then displays the percentage of freight charges in each subtotal. This expression uses the Sum function to total the values in the Freight field, and then divides those totals by the sum of the values in the Subtotal field. To use this expression, you must convert your select query into a Totals query because you need to use the Total row in the design grid, and you must set the Total cell for this field to Expression. For more information about creating a Totals query, see the article Sum data by using a query. If you set the Format property of the field to Percent, do not include *100. |
For more information about using aggregate functions and totaling the values in field and columns, see the articles Sum data by using a query, Count data by using a query, Display column totals in a datasheet using a Totals row, and Display column totals in a datasheet.
Date operations
Nearly all databases store and track dates and times. You work with dates and times in Access by setting the date and time fields in your tables to 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.
| Expression | Description |
|---|---|
| LagTime: DateDiff("d", [OrderDate], [ShippedDate]) | Creates a field called LagTime, and then uses the DateDiff function to display the number of days between the order date and ship date. |
| YearHired: DatePart("yyyy",[HireDate]) | Creates a field called YearHired, and then uses the DatePart function to display the year each employee was hired. |
| MinusThirty: Date( )- 30 | Creates a field called MinusThirty, and then uses the Date function to display the date 30 days prior to the current date. |
SQL aggregate functions
The expressions in the following table use SQL (Structured Query Language) functions that aggregate or summarize data. You often see these functions (for example, Sum, Count, and Avg) referred to as aggregate functions.
In addition to aggregate functions, Access also provides "domain" aggregate functions that you use to sum or count values selectively. For example, you can count only the values within a certain range or look up a value from another table. The set of domain aggregate functions includes the DSum Function, the DCount Function, and the DAvg Function.
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.
| Expression | Description |
|---|---|
| RowCount: Count(*) | Creates a field called RowCount, and then 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 | Creates a field called FreightPercentage, and then calculates 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.) You must use this expression with a Totals query. If you set the Format property of the field to Percent, do not include *100. For more information about creating a Totals query, see the article Sum data by using a query. |
| AverageFreight: DAvg("[Freight]", "[Orders]") | Creates a field called AverageFreight, and then uses the DAvg function to calculate the average freight on all orders combined in a Totals query. |
Fields with missing data
The expressions shown here work with fields with potentially missing information, such as those containing null (unknown or undefined) values. You frequently encounter null values, such as an unknown price for a new product or a value that a coworker forgot to add to an order. The ability to find and process null values can be a critical part of database operations, and the expressions in the following table demonstrate some common ways to deal with null values.
| Expression | Description |
|---|---|
| CurrentCountryRegion: IIf(IsNull([CountryRegion]), " ", [CountryRegion]) | Creates a field called CurrentCountryRegion, and then uses the IIf and IsNull functions to display an empty string in that field when the CountryRegion field contains a null value; otherwise, it displays the contents of the CountryRegion field. |
| LeadTime: IIf(IsNull([RequiredDate] - [ShippedDate]), "Check for a missing date", [RequiredDate] - [ShippedDate]) | Creates a field called LeadTime, and then uses the IIf and IsNull functions to display the message "Check for a missing date" if the value in either the RequiredDate field or the ShippedDate field is null; otherwise, it displays the date difference. |
| SixMonthSales: Nz([Qtr1Sales]) + Nz([Qtr2Sales]) | Creates a field called SixMonthSales, and then displays the total of the values in the Qtr1Sales and Qtr2Sales fields by first using the Nz function to convert any null values to zero. |
Calculated fields with subqueries
You can use a nested query, also called a subquery, to create a calculated field. The expression in the following table is one example of a calculated field that results from a subquery.
| Expression | Description |
|---|---|
| Cat: (SELECT [CategoryName] FROM [Categories] WHERE [Products].[CategoryID]=[Categories].[CategoryID]) | Creates a field called Cat, and then displays the CategoryName, if the CategoryID from the Categories table is the same as the CategoryID from the Products table. |
Match text values
The sample expressions in this table demonstrate 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. |
| ShipCountryRegion | In("Canada", "UK") | Uses the In operator to display orders shipped to Canada or the UK. |
| ShipCountryRegion | Not "USA" | Uses the Not operator to display orders shipped to countries/regions other than USA. |
| ProductName | Not Like "C*" | Uses the Not operator and the * wildcard character to display products whose names do not begin with C. |
| CompanyName | >="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. |
Match date criteria
The expressions in the following table demonstrate the use of dates and related functions in criteria expressions. For more information about entering and using date values, see the article Enter a date or time value.
| Field | Expression | Description |
|---|---|---|
| ShippedDate | #2/2/2017# | Displays orders shipped on February 2, 2017. |
| ShippedDate | Date() | Displays orders shipped today. |
| RequiredDate | 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's date. |
| OrderDate | < Date( ) - 30 | Uses the Date function to display orders more than 30 days old. |
| OrderDate | Year([OrderDate])=2017 | Uses the Year function to display orders with order dates in 2017. |
| 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. |
| ShippedDate | Between #1/5/2017# And #1/10/2017# | Uses the Between...And operator to display orders shipped no earlier than 5-Jan-2017 and no later than 10-Jan-2017. |
| RequiredDate | Between Date( ) And DateAdd("M", 3, Date( )) | Uses the Between...And operator 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 employees who have birthdays this month. |
Find missing data
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 | Expression | Description |
|---|---|---|
| ShipRegion | Is Null | Displays orders for customers whose ShipRegion field is null (missing). |
| ShipRegion | 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. |
Match record patterns with Like
The Like operator provides a great deal of flexibility when you are trying to match rows that follow a pattern, because you can use Like with wildcard characters and 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. For example, you use the expression Like "S*" to find all names that begin with the letter S. For more information, see the article Like Operator.
| Field | Expression | Description |
|---|---|---|
| ShipName | Like "S*" | Finds all records in the ShipName field that start with the letter S. |
| ShipName | Like "*Imports" | Finds all records in the ShipName field that end with the word "Imports". |
| ShipName | Like "[A-D]*" | Finds all records in the ShipName field that begin with the letters A, B, C, or D. |
| ShipName | Like "*ar*" | Finds all records in the ShipName field that include the letter sequence "ar". |
| ShipName | Like "Maison Dewe?" | Finds all records in the ShipName field that include "Maison" in the first part of the value and a five-letter string in which the first four letters are "Dewe" and the last letter is unknown. |
| ShipName | Not Like "A*" | Finds all records in the ShipName field that do not start with the letter A. |
Match rows with SQL aggregates
You use an SQL or domain aggregate function when you need to sum, count, or average values selectively. For example, you might want to count only those values that fall 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. The sample expressions in the following table use the domain aggregate functions to perform a calculation on a set of values, and use the result as the query criteria.
| Field | Expression | Description |
|---|---|---|
| Freight | > (DStDev("[Freight]", "Orders") + DAvg("[Freight]", "Orders")) | Uses the DStDev and DAvg functions to display all orders for which the freight cost rose above the mean plus the standard deviation for freight cost. |
| Quantity | > DAvg("[Quantity]", "[Order Details]") | Uses the DAvg function to display products ordered in quantities above the average order quantity. |
Match fields with subqueries
You use a subquery, also called a nested query, to calculate a value for use as a criterion. The sample expressions in the following table match rows based on the results returned by 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 sales representative whose salary is higher than that of all employees with "Manager" or "Vice President" in their titles. |
| OrderTotal: [UnitPrice] * [Quantity] | > (SELECT AVG([UnitPrice] * [Quantity]) FROM [Order Details]) | Orders with totals that are higher than the average order value. |
Update queries
You use an update query to modify the data in one or more existing fields in a database. For example, you can replace values or delete them entirely. This table demonstrates some ways to use expressions in update queries. You use these expressions in the Update To row in the query design grid for the field that you want to update.
For more information about creating update queries, see the article Create and run an update query.
| Field | Expression | Result |
|---|---|---|
| Title | "Salesperson" | Changes a text value to Salesperson. |
| ProjectStart | #8/10/17# | Changes a date value to 10-Aug-17. |
| 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. |
| LineItemTotal | [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. |
| ShipPostalCode | Right([ShipPostalCode], 5) | Truncates the leftmost characters, leaving the five rightmost characters. |
| UnitPrice | Nz([UnitPrice]) | Changes a null (undefined or unknown) value to a zero (0) in the UnitPrice field. |
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 statement 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]="Danseglio"; | Displays the values in the FirstName and LastName fields for employees whose last name is Danseglio. |
| SELECT [ProductID],[ProductName] FROM [Products] WHERE [CategoryID]=Forms![New Products]![CategoryID]; | Displays the values in the ProductID and ProductName fields in the Products table for records 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. |
Table expressions
The two most common ways to use expressions in tables are to assign a default value and to create a validation rule.
Field default values
When you design a database, you might want to assign a default value to a field or control. Access then supplies the default value when a new record containing the field is created or when an object that contains the control is created. The expressions in the following table represent the sample default values for a field or control. 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 containing a null value |
| Order Date | Date( ) | Today's date |
| DueDate | Date() + 60 | The date 60 days forward from today |
Field validation rules
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.
| 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. |
| < #1/1/2017# | Enter a date prior to 1/1/2017. |
| >= #1/1/2017# And < #1/1/2008# | Date must occur in 2017. |
For more information about validating data, see the article Create a validation rule to validate data in a field.
Macro 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
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.
Tip To force Access to temporarily ignore an action, type False as a condition. This can be helpful when you are trying to find problems in a macro.
| 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 Orders form. |
| [ShippedDate] Between #2-Feb-2017# And #2-Mar-2017# | The value of the ShippedDate field on the form from which the macro is run is no earlier than 2-Feb-2017 and no later than 2-Mar-2017. |
| 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. |
| [CountryRegion]="UK" And Forms![SalesTotals]![TotalOrds] > 100 | The value in the CountryRegion 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. |
| [CountryRegion] In ("France", "Italy", "Spain") And Len([PostalCode])<>5 | The value in the CountryRegion field on the form from which the macro is run is either France, Italy, or Spain, and the postal code is not 5 characters 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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