In some cases, the name of an element works by itself as an identifier. For instance, the identifier for a field includes the name of the field and the name of the table to which the field belongs. An identifier includes the name of the element that you are identifying and also the name of the element to which it belongs. When you use an object, collection, or property in an expression, you refer to that element by using an identifier. The following diagram illustrates the relationship between collections, objects, and properties: For example, a query object has a Default View property that both describes and lets you specify how the query will appear when you run it. Objects have properties, which describe, and provide a way to change, the object's characteristics. For example, a table object is a collection that contains field objects. Some objects that are a member of a collection in your database can also be collections that contain other objects. For example, the set of all tables in a database is a collection. The set of all members of a particular type of object is known as a collection. When you create a new object, you give it a name. Some objects are already named, such as the Contacts table in a database created from the Microsoft Office Access Contacts template. Top of Page Objects, collections, and propertiesĪll of the tables, queries, forms, reports, and fields in an Access database are individually known as objects. Values Values can occur in many locations in an expression. There are exceptions to this form, as detailed in the Operators section.Ĭonstants The general form is: Identifier comparison_operator constant Operators The general form is: Identifier operator identifier For more information, see Functions (arranged by category).
Before you use a particular function, review that function's syntax. One of the arguments is usually an identifier or an expression. įunctions The general form is: Function(argument, argument) It is not uncommon for an identifier to take the form. You only have to specify enough parts of an identifier to make it unique in the context of your expression. You can also use an expression as part of another expression - typically as an argument of a function. Any valid expression must contain at least one function or at least one identifier, and can also contain constants or operators. To build an expression, you combine identifiers by using functions, operators, constants, and values. You can also use expressions in the Validation Rule property for a table field. For example, you can use expressions in the Control Source and Default Value properties for a control. Tables, queries, forms, reports, and macros all have properties that accept an expression. Expressions are used in many places to perform calculations, manipulate characters, or test data. You can use this expression in the Validation Rule property of a control or table field to ensure that only positive values are entered. True when it is compared to a number that is greater than 0.įalse when it is compared to a number that is less than 0. For example, this Boolean expression consists of just an operator and a constant: >0 This expression can be used in a text box in a form footer or report footer to calculate sales tax for a group of items.Įxpressions can be much more complex or much simpler than this example. The nesting limit for expressions in a web database is 65Īn expression is a combination of some or all of the following: built-in or user-defined functions, identifiers, operators, values, and constants that evaluate to a single value.įor example, the following expression contains common components: =Sum()*0.08 In this articleįunctions, operators, constants, and values But with a good understanding of expression syntax and a little practice, it becomes much easier.
Initially, expressions in Access are a little bit hard to read. Syntax is the set of rules by which the words and symbols in an expression are correctly combined. To use expressions, you write them by using proper syntax.
You can calculate these values by using expressions. For example, you want to calculate sales tax on an order, or calculate the total value of the order itself. When you use Microsoft Access, you often need to work with values that are not directly in your data.
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