What does expression mean in access




















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.

Creates a field called TypeCode, and then uses the Right function to display the last two characters of the values in the AssetCode field.

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. Names the calculated field ExtendedPrice, and uses the CCur function to calculate the line item totals with an applied discount. You can also perform arithmetic operations on dates. Creates a field called PrimeFreight, and then displays freight charges plus 10 percent in the field. Creates a field called OrderAmount, and then displays the product of the values in the Quantity and UnitPrice fields.

Creates a field called LeadTime, and then displays the difference between the values in the RequiredDate and ShippedDate fields. 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.

Nearly all databases store and track dates and times. 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. Creates a field called LagTime, and then uses the DateDiff function to display the number of days between the order date and ship date. Creates a field called YearHired, and then uses the DatePart function to display the year each employee was hired.

Creates a field called MinusThirty, and then uses the Date function to display the date 30 days prior to the current date. 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.

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. 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. 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. Creates a field called AverageFreight, and then uses the DAvg function to calculate the average freight on all orders combined in a Totals query.

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. 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.

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.

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. 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. The sample expressions in this table demonstrate criteria that match whole or partial text values.

Uses the Or operator to display orders shipped to London or Hedge End. Uses the In operator to display orders shipped to Canada or the UK. Displays orders shipped to companies whose names start with the letters N through Z. Uses the Right function to display orders with ProductCode values that end in Displays orders shipped to customers whose names start with the letter S. 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 Format a date and time field. 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.

Uses the Year and Month functions and the And operator to display orders for the current year and month. And operator to display orders shipped no earlier than 5-Jan and no later than Jan And operator to display orders required between today's date and three months from today's date. 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.

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. 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 more information, see the article Like Operator. 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. 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. 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.

Uses the DAvg function to display products ordered in quantities above the average order quantity. 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.

Salary of every sales representative whose salary is higher than that of all employees with "Manager" or "Vice President" in their titles. 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. Every query that you create in query Design view can also be expressed by using SQL. The following table shows sample SQL statements that employ an expression. Calculates the average extended price for orders for which the value in the ExtendedPrice field is more than , and displays it in a field named Average Extended Price.

In a field named CountOfProductID, displays the total number of products for categories with more than 10 products. The two most common ways to use expressions in tables are to assign a default value and to create a validation rule. 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.

New York, N. Note that you must enclose the value in quotation marks if it includes punctuation. To quickly find the functions you want, Access provides a tool called the Expression Builder. To launch the Expression Builder, follow these steps:.

Most Access experts find that the Expression Builder is too clunky to be worth the trouble. But even though the Expression Builder may not be the most effective way to write an expression, it's a great way to learn about new and mysterious functions, thanks to its built-in function reference. If you find a function that sounds promising but you need more information, select it in the list and then click Help.

You'll be rewarded with a brief summary that explains the purpose of the function and the arguments you need to supply. In the following sections you'll see the most useful functions for working with numbers, text, and dates. To discover even more functions, use the Expression Builder. You can calculate these values by using expressions.

To use expressions, you write them by using proper syntax. Syntax is the set of rules by which the words and symbols in an expression are correctly combined. Initially, expressions in Access are a little bit hard to read.

But with a good understanding of expression syntax and a little practice, it becomes much easier. Overview of expressions. Components of expressions. Objects, collections, and properties. Functions, operators, constants, and values. The nesting limit for expressions in a web database is An 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.

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. Expressions can be much more complex or much simpler than this example. For example, this Boolean expression consists of just an operator and a constant:.

True when it is compared to a number that is greater than 0. False when it is compared to a number that is less than 0. You can use this expression in the Validation Rule property of a control or table field to ensure that only positive values are entered. Expressions are used in many places to perform calculations, manipulate characters, or test data. Tables, queries, forms, reports, and macros all have properties that accept an expression.

For example, you can use expressions in the Control Source and Default Value properties for a control. You can also use expressions in the Validation Rule property for a table field. To build an expression, you combine identifiers by using functions, operators, constants, and values. Any valid expression must contain at least one function or at least one identifier, and can also contain constants or operators.

You can also use an expression as part of another expression — typically as an argument of a function. This is called nesting an expression.

You only have to specify enough parts of an identifier to make it unique in the context of your expression. It is not uncommon for an identifier to take the form [Object name]. One of the arguments is usually an identifier or an expression. Some functions do not require arguments. Before you use a particular function, review that function's syntax. For more information, see Functions arranged by category. There are exceptions to this form, as detailed in the Operators section.

Values Values can occur in many locations in an expression. All of the tables, queries, forms, reports, and fields in an Access database are individually known as objects.

Every object has a name. Some objects are already named, such as the Contacts table in a database created from the Microsoft Office Access Contacts template. When you create a new object, you give it a name. The set of all members of a particular type of object is known as a collection. For example, the set of all tables in a database is a collection.

Some objects that are a member of a collection in your database can also be collections that contain other objects.

For example, a table object is a collection that contains field objects. Objects have properties , which describe, and provide a way to change, the object's characteristics.

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.

When you use an object, collection, or property in an expression, you refer to that element by using an identifier. An identifier includes the name of the element that you are identifying and also the name of the element to which it belongs. 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 example of such an identifier is:. In some cases, the name of an element works by itself as an identifier.

This is true when the name of the element is unique in the context of the expression that you are creating. The rest of the identifier is implied by the context. For example, if you are designing a query that uses only one table, the field names alone will work as identifiers, because the field names in a table must be unique in that table.

Because you are using only one table, the table name is implied in any identifier that you use in the query to refer to a field. In other cases, you must be explicit about the parts of an identifier for a reference to work. This is true when an identifier is not unique in the context of the expression.

When there is ambiguity, you must explicitly denote enough parts of the identifier to make it unique in context.



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