Access: User-defined Functions
Do you ever use the same equation in several places or write long formulas with complex logic? Increase clarity by creating your own custom user-defined function (UDF) in VBA. Once a function is defined, it can be used throughout the database in queries, forms, and reports and even called by code.
A function returns a value. Access already has built-in functions such as SUM, which shows the result of adding several numbers, and COUNT, which returns how many values there are. A function can be used in place of a value in an expression for a field in a query, a control source on a form or report, and more. The logic for writing a function is the same as for creating a formula.
Let’s write a function to return the maximum value from a set of two numbers or dates. If one of the pair is missing, then the other should be returned. If neither has a value, the result will be null.
WRITING A FUNCTION
Press Alt+F11 to go to the Visual Basic Editor. Create a new module. From the menu, select Insert, Module. At the top of the new module, it will say “Option Compare Database.” Option statements are instructions that apply to the whole module. This one tells the code how to compare string data. “Option Explicit” can be added to require that all variable names be defined. That way, if your code contains any misspelled variables, the error will be identified when the code is compiled. Otherwise, it could create problems (run-time errors) when the code is used, such as in a function or query. Functions and Subs are defined below the Option statements.
Figure 1 shows a function called GetMax. The first line after the option statements begins with “Function GetMax” to declare a function and define the name. After this are parentheses, which can be empty or contain arguments (parameters). In this case, there are two arguments containing the values to be compared: pvValue1 and pvValue2. Finally, the data type of the return value is specified “As Variant.” Variant provides flexibility for different types of data and to handle a null result. Not only will the GetMax function work for numbers and dates, it will also work for strings. For example, GetMax(5,1) will return a value of 5, GetMax(Date(),#1/1/#) will give today’s date, and GetMax(abc,def) will return “def.”
The return value is assigned to the function name. In the code, GetMax=pvValue1 means that the value returned for the GetMax function will be the value pvValue1, which is the first parameter.
Enter the function in Figure 1 into the module. When done, go to the menu and select Debug, Compile to compile the code and see if there are any errors. Once any errors are resolved and everything is correct, save the module. It’s a good idea to use a prefix such as “mod” when naming a module to ensure the module name is different than any name used by any other procedure, such as a function. In this case, since the module only has one function, it will be called “mod_GetMax.”
One place to use the UDF is in a query. For example, in our database for customer payments, the qCustomerBalance query contains separate columns for the last date a customer ordered something and for the last date a payment was made. Using the GetMax function, we can add a column named LastActivity to show the most recent date there was any activity by adding a field that contains LastActivity: GetMax( [MaxDateOrder], [MaxDatePay] ).
UPDATE A TABLE
The Products table of our database has a field called SerialNum that corresponds to the plate on each custom product that the company makes. There are values like BN, PSLB, and EBN The first part of the serial number is the manufacture date in YYMMDD format. The second part corresponds to the base model, such as BN, PLSB, or EBN. If you wanted to use the second part to fill a short text field called Model, you could build a function as shown in Figure 2.
Called GetStringPart, the function returns part of a string. It uses the Split function to separate parts of a string into an array of values. Since the first array index is zero (0), one (1) is subtracted from the part number passed. A specific array element is referenced by putting its element number in parentheses following the array name. The third parameter is optional and specifies what delimiter to use for splitting, which by default will be a dash.
GetStringPart can be used in an SQL statement to update the Model field in the Products table with the relevant part of the serial number:
UPDATE PRODUCTS Products
SET Products.Model = GetStringPart( [SerialNum], 2, - )
WHERE ( Products.SerialNum Is Not Null );
Functions used in a query must specify all parameters, even the optional ones. Even though the procedure defines the delimiter to be optional (Optional psDeli As String = -) and defaults to a dash, which is what we want, query expressions must still include the parameter.
Download this month’s database: SF__UDFs.
User-defined functions are reusable and easier to comprehend than complex formulas.
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MS Access - Built-In Functions
In this chapter, we will be working with Built-in Functions. In Access, there are close to a hundred built-in functions and it is almost impossible to cover every single one of them. In this chapter, we will cover the basic structure, syntax, and use some of the more popular functions, and also the pitfalls, so that you can go exploring some of the other functions on your own.
A function is a VBA procedure that performs a task, or calculation, and returns a result. Functions can generally be used in queries, but there are other places that you can use functions.
You can use functions in table properties, for example, if you want to specify a default value for a date/time field, you can use the date or the Now function to call up the current date/time information from your system, and input that value automatically.
You can also use functions in an expression when you create a calculated field, or use the functions inside form or report controls. You can use functions even in macro arguments.
Functions can be quite simple, requiring no other information to be called, or, simply reference one field from a table or query.
On the other hand, they can also get quite complicated, with multiple arguments, field references, and even other functions nested inside another function.
Let us now look into some examples of using built-in functions.
Date & Time Functions
Let us now understand the Date and Time functions −
The Date() function is designed to return the current system date. This function does not require any function arguments or additional information. All you have to do is write the name of the function and those open and close parentheses.
There are two very similar built-in functions Time() and Now().
The Time() Function returns the current system time only and the Now() Function returns both the current system date and time.
Depending on the data that you want to track, or store, or query, you have three built-in, easy-to-use functions to help with that task.
Let us now open your database and create a new query using query design and add tblProjects and tblTasks.
Add ProjectName from tblProjects and TaskTitle, StartDate and DueDate from tblTasks and run your query.
You can now see all the different tasks from all projects. If you want to view the project tasks that are in progress as on today’s date, then we have to specify a criterion using a Date() Function to look at projects that start on or after today's date.
Let us now specify the criteria underneath the StartDate.
The criteria starts with an operator greater than symbol, followed by an equal to symbol and then Date Function.
When we run this query, all the tasks will occur either on today's date or in the future as in the following screenshot.
This was an example of how you can use the Date() function as query criteria.
Let us now say this query needs to be more flexible in terms of the dates it is pulling starting this week.
We do have a couple of different tasks that began this week, that are not showing up in this current list, because of our criteria. It's looking at start dates that are equal to today or above.
If we want to view the tasks that started this week, that have not yet completed or should complete today, let us go back to the Design View.
Here, we will add some additional information to these criteria. In fact, we want it greater than or equal to today's date minus seven days.
If we type minus seven and run the query, you can see the tasks that started this week as well.
The DateDiff() Function is another very popular date/time function. The DateDiff Function returns a Variant (long), specifying the number of time intervals between two specified dates. In other words, it calculates the difference between two dates, and you get to pick the interval by which the function calculates that difference.
Let us now say we want to calculate our authors' age. For this, we first we need to create a new query and add our authors table and then add FirstName, LastName, and the BirthDay fields.
We can calculate people's age by calculating the difference between their date of birth, or birthday and whatever today's date is.
Let us try using the DateDiff Function in a new field.
Let us call it Age followed by a colon, and then write DateDiff Function.
- The first function argument for the DateDiff function is the interval, so type “yyyy”.
- The next function argument is the first date that we want to calculate by, which, in this case, will be the Birthday field.
- The third function argument is whatever today's date is.
Now, run your query and you will see the new field which shows the age of each author.
The Format() Function returns a string, containing an expression formatted according to instructions contained in a format expression. Here is the list of user-defined formats which can be used in Format() function.ss
|y||Day of year|
Let us now go back to your query and add more fields in the same using the Format() function.
Type the Format Function. The first function argument will be an expression, which can be almost anything. Let us now have the birthday field as the first and the next thing is to write our format. In this case, we need month, month, day, day. Write “mmdd” in quotes and then, run your query.
It is now taking the date from the birthday field, 4 is the month and 17 is the day.
Let us add “mmm” and “mmmm” instead of “mmdd” in the next fields as in the following screenshot.
Run your query and you will see the results as in the following screenshot.
In the next field, it is returning the first 3 character from the name of the month for that birthday and in the last field you will get the full month name.
To see the month followed by year from birthday, let us add the “yyyy” as well as shown in the following screenshot.
Let us run your query again.
You will now see the month followed by a comma and then the year.
The IIf() Function is an abbreviation for “Immediate If” and this function evaluates an expression as either true or false and returns a value for each. It has up to three function arguments, all of which are required.
- The first argument is any expression that you want to evaluate.
- The next argument stands for the true part, which can be a value or an expression returned if your first expression is true.
- The last argument is what you want returned if your expression is false.
Let us take a simple example. We will create a new query using query design and add tblAuthors table and then add the following fields.
You can now see we have three fields — FirstName, MiddleInitial, LastName, and then this concatenated field, which is pulling all three fields together. Let us run your query to see the result of this query.
Now, you can see the result of the query, but you will also notice that some records do not have a middle initial. For example, the Joyce Dyer record does not have a middle initial, but in the FullName field you will see the period that really doesn't need to be there. So, go back to the Design View. Here, we will concatenate the name in a different way using the IIf Function.
Let us write the name in another field and call it FullName1 and then type the IIf function.
The first function argument for the Immediate If function is going to be your expression. In the expression, we will see if the middle initial field is blank or is null.
The next argument is the true part. So, if the middle initial is null then we would want to display the FirstName and the LastName.
Now, for our false part — if the MiddleInitial is not null, then we would want to display the FirstName, MiddleInitial, and LastName.
Let us now run your query and you will see the results as in the following screenshot.
MS Access: Functions - Listed by Category
For easy reference, we have provided a list of all Microsoft Access functions. The list of Access functions is sorted into the type of function based on categories such as string, numeric/mathematical, date/time, advanced/logical, domain aggregate, data type conversion, group by, and file/directory functions.
It is important to note that there are 2 type of functions in Access - functions used in SQL/Queries and functions used in VBA code. Some functions can be used as both, but some can not.
Below is the list of MSAccess functions, sorted by category (ie: type of function).
Data Type Conv. Functions
Group By Functions
Test a string for an alphanumeric valueConvert currency into wordsConvert Bangladesh taka currency into wordsCreating a custom round functionRetrieve the user name from Windows while in an Access database
This article contains links to articles that provide details about common functions used in expressions in Microsoft Access. They are arranged first by group and then are arranged alphabetically at the end of this article.
Tip: Beginning with Access , the Expression Builder has IntelliSense, so you can see what arguments your expression requires.
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Type Conversion Functions
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DFirst, DLast Functions
DMin, DMax Functions
DStDev, DStDevP Functions
DVar, DVarP Functions
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Int, Fix Functions
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Min, Max Functions
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Var, VarP Functions
LTrim, RTrim, and Trim Functions
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DMin, DMax Functions
DStDev, DStDevP Functions
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Int, Fix Functions
LTrim, RTrim, and Trim Functions
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StDev, StDevP Functions
Type Conversion Functions
Var, VarP Functions
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Function ms access
Database manager that is part of the Microsoft Office package
Microsoft Access is a database management system (DBMS) from Microsoft that combines the relationalMicrosoft Jet Database Engine with a graphical user interface and software-development tools. It is a member of the Microsoft suite of applications, included in the Professional and higher editions or sold separately.
Microsoft Access stores data in its own format based on the Access Jet Database Engine. It can also import or link directly to data stored in other applications and databases.
Software developers, data architects and power users can use Microsoft Access to develop application software. Like other Microsoft Office applications, Access is supported by Visual Basic for Applications (VBA), an object-based programming language that can reference a variety of objects including the legacy DAO (Data Access Objects), ActiveX Data Objects, and many other ActiveX components. Visual objects used in forms and reports expose their methods and properties in the VBA programming environment, and VBA code modules may declare and call Windows operating system operations.
Prior to the introduction of Access, Borland (with Paradox and dBase) and Fox (with FoxPro) dominated the desktop database market. Microsoft Access was the first mass-market database program for Windows. With Microsoft's purchase of FoxPro in and the incorporation of Fox's Rushmore query optimization routines into Access, Microsoft Access quickly became the dominant database for Windows—effectively eliminating the competition which failed to transition from the MS-DOS world.
Microsoft's first attempt to sell a relational database product was during the mid s, when Microsoft obtained the license to sell R:Base. In the late s Microsoft developed its own solution codenamed Omega. It was confirmed in that a database product for Windows and OS/2 was in development. It was going to include the "EB" Embedded Basic language, which was going to be the language for writing macros in all Microsoft applications, but the unification of macro languages did not happen until the introduction of Visual Basic for Applications (VBA). Omega was also expected to provide a front end to the Microsoft SQL Server. The application was very resource-hungry, and there were reports that it was working slowly on the processors that were available at the time. It was scheduled to be released in the 1st quarter of , but in the development of the product was reset and it was rescheduled to be delivered no sooner than in January  Parts of the project were later used for other Microsoft projects: Cirrus (codename for Access) and Thunder (codename for Visual Basic, where the Embedded Basic engine was used). After Access's premiere, the Omega project was demonstrated in to several journalists and included features that were not available in Access.
After the Omega project was scrapped, some of its developers were assigned to the Cirrus project (most were assigned to the team which created Visual Basic). Its goal was to create a competitor for applications like Paradox or dBase that would work on Windows. After Microsoft acquired FoxPro, there were rumors that the Microsoft project might get replaced with it, but the company decided to develop them in parallel. It was assumed that the project would make use of Extensible Storage Engine (Jet Blue) but, in the end, only support for Microsoft Jet Database Engine (Jet Red) was provided. The project used some of the code from both the Omega project and a pre-release version of Visual Basic. In July , betas of Cirrus shipped to developers and the name Access became the official name of the product. "Access" was originally used for an older terminal emulation program from Microsoft. Years after the program was abandoned, they decided to reuse the name here.
Microsoft released Access version on November 13, , and an Access release in May to improve compatibility with other Microsoft products and to include the Access Basic programming language.
Microsoft specified the minimum hardware requirements for Access v as: Microsoft Windows v with 4 MB of RAM required, 6 MB RAM recommended; 8 MB of available hard disk space required, 14 MB hard disk space recommended. The product shipped on seven MB diskettes. The manual shows a copyright date.
As a part of the Microsoft Office Professional with Book Shelf, Microsoft Access was included with first sample databases "NorthWind Trader" which covered every possible aspect of programming your own database. The Northwind Traders sample first introduced the Main Switchboard features new to Access for The photo of Andrew Fuller, record #2 of that sample database was the individual that presented and worked with Microsoft to provide such an outstanding example database.
With Office 95, Microsoft Access (a.k.a. "Access 95") became part of the Microsoft Office Professional Suite, joining Microsoft Excel, Word, and PowerPoint and transitioning from Access Basic to VBA. Since then, Microsoft has released new versions of Microsoft Access with each release of Microsoft Office. This includes Access 97 (version ), Access (version ), Access (version ), Access (version ), Access (version ), Access (version ), and Access (version ).
Versions and of Microsoft Jet Database Engine (used by Access and the later-released Access 97 respectively) had a critical issue which made these versions of Access unusable on a computer with more than 1 GB of memory. While Microsoft fixed this problem for Jet /Access 97 post-release, it never fixed the issue with Jet /Access
The native Access database format (the Jet MDB Database) has also evolved over the years. Formats include Access , , , , 97, , , and The most significant transition was from the Access 97 to the Access format; which is not backward compatible with earlier versions of Access. As of [update] all newer versions of Access support the Access format. New features were added to the Access format which can be used by Access , , , and
Microsoft Access increased the maximum database size to 2GB from 1GB in Access
Microsoft Access introduced a new database format: ACCDB. It supports links to SharePoint lists and complex data types such as multivalue and attachment fields. These new field types are essentially recordsets in fields and allow the storage of multiple values or files in one field. Microsoft Access also introduced File Attachment field, which stored data more efficiently than the OLE (Object Linking and Embedding) field.
Microsoft Access offers traditional Access desktop applications plus a significantly updated SharePoint web service. The Access Web model in Access was replaced by a new architecture that stores its data in actual SQL Server databases. Unlike SharePoint lists, this offers true relational database design with referential integrity, scalability, extensibility and performance one would expect from SQL Server. The database solutions that can be created on SharePoint offer a modern user interface designed to display multiple levels of relationships that can be viewed and edited, along with resizing for different devices and support for touch. The Access desktop is similar to Access but several features were discontinued including support for Access Data Projects[clarification needed] (ADPs), pivot tables, pivot charts, Access data collections, source code control, replication, and other legacy features. Access desktop database maximum size remained 2GB (as it has been since the version).
In addition to using its own database storage file, Microsoft Access also may be used as the 'front-end' of a program while other products act as the 'back-end' tables, such as Microsoft SQL Server and non-Microsoft products such as Oracle and Sybase. Multiple backend sources can be used by a Microsoft Access Jet Database (ACCDB and MDB formats). Similarly, some applications such as Visual Basic, ASP.NET, or Visual Studio .NET will use the Microsoft Access database format for its tables and queries. Microsoft Access may also be part of a more complex solution, where it may be integrated with other technologies such as Microsoft Excel, Microsoft Outlook, Microsoft Word, Microsoft PowerPoint and ActiveX controls.
Access tables support a variety of standard field types, indices, and referential integrity including cascadingupdates and deletes. Access also includes a query interface, forms to display and enter data, and reports for printing. The underlying Jet database, which contains these objects, is multi-user and handles record-locking.
Repetitive tasks can be automated through macros with point-and-click options. It is also easy to place a database on a network and have multiple users share and update data without overwriting each other's work. Data is locked at the record level which is significantly different from Excel which locks the entire spreadsheet.
There are template databases within the program and for download from Microsoft's website. These options are available upon starting Access and allow users to enhance a database with predefined tables, queries, forms, reports, and macros. Database templates support VBA code but Microsoft's templates do not include VBA code.
Programmers can create solutions using VBA, which is similar to Visual Basic (VB6) and used throughout the Microsoft Office programs such as Excel, Word, Outlook and PowerPoint. Most VB6 code, including the use of Windows API calls, can be used in VBA. Power users and developers can extend basic end-user solutions to a professional solution with advanced automation, data validation, error trapping, and multi-user support.
The number of simultaneous users that can be supported depends on the amount of data, the tasks being performed, level of use, and application design. Generally accepted limits are solutions with 1 GB or less of data (Access supports up to 2 GB) and it performs quite well with or fewer simultaneous connections ( concurrent users are supported). This capability is often a good fit for department solutions. If using an Access database solution in a multi-user scenario, the application should be "split". This means that the tables are in one file called the back end (typically stored on a shared network folder) and the application components (forms, reports, queries, code, macros, linked tables) are in another file called the front end. The linked tables in the front end point to the back end file. Each user of the Access application would then receive his or her own copy of the front end file.
Applications that run complex queries or analysis across large datasets would naturally require greater bandwidth and memory. Microsoft Access is designed to scale to support more data and users by linking to multiple Access databases or using a back-end database like Microsoft SQL Server. With the latter design, the amount of data and users can scale to enterprise-level solutions.
Microsoft Access's role in web development prior to version is limited. User interface features of Access, such as forms and reports, only work in Windows. In versions through an Access object type called Data Access Pages created publishable web pages. Data Access Pages are no longer supported. The Microsoft Jet Database Engine, core to Access, can be accessed through technologies such as ODBC or OLE DB. The data (i.e., tables and queries) can be accessed by web-based applications developed in ASP.NET, PHP, or Java. With the use of Microsoft's Terminal Services and Remote Desktop Application in Windows Server R2, organizations can host Access applications so they can be run over the web. This technique does not scale the way a web application would but is appropriate for a limited number of users depending on the configuration of the host.
Access allows databases to be published to SharePoint web sites running Access Services. These web-based forms and reports run in any modern web browser. The resulting web forms and reports, when accessed via a web browser, don't require any add-ins or extensions (e.g. ActiveX, Silverlight).
Access can create web applications directly in SharePoint sites running Access Services. Access web solutions store its data in an underlying SQL Server database which is much more scalable and robust than the Access version which used SharePoint lists to store its data.
Access Services in SharePoint has since been retired.
A compiled version of an Access database (File extensions: .MDE /ACCDE or .ADE; ACCDE only works with Access or later) can be created to prevent user from accessing the design surfaces to modify module code, forms, and reports. An MDE or ADE file is a Microsoft Access database file with all modules compiled and all editable source code removed. Both the .MDE and .ADE versions of an Access database are used when end-user modifications are not allowed or when the application's source code should be kept confidential.
Microsoft also offers developer extensions for download to help distribute Access applications, create database templates, and integrate source code control with Microsoft Visual SourceSafe.
Users can create tables, queries, forms and reports, and connect them together with macros. Advanced users can use VBA to write rich solutions with advanced data manipulation and user control. Access also has report creation features that can work with any data source that Access can access.
The original concept of Access was for end users to be able to access data from any source. Other features include: the import and export of data to many formats including Excel, Outlook, ASCII, dBase, Paradox, FoxPro, SQL Server and Oracle. It also has the ability to link to data in its existing location and use it for viewing, querying, editing, and reporting. This allows the existing data to change while ensuring that Access uses the latest data. It can perform heterogeneousjoins between data sets stored across different platforms. Access is often used by people downloading data from enterprise level databases for manipulation, analysis, and reporting locally.
There is also the Jet Database format (MDB or ACCDB in Access ) which can contain the application and data in one file. This makes it very convenient to distribute the entire application to another user, who can run it in disconnected environments.
One of the benefits of Access from a programmer's perspective is its relative compatibility with SQL (structured query language)—queries can be viewed graphically or edited as SQL statements, and SQL statements can be used directly in Macros and VBA Modules to manipulate Access tables. Users can mix and use both VBA and "Macros" for programming forms and logic and offers object-oriented possibilities. VBA can also be included in queries.
Microsoft Access offers parameterized queries. These queries and Access tables can be referenced from other programs like VB6 and .NET through DAO or ADO. From Microsoft Access, VBA can reference parameterized stored procedures via ADO.
The desktop editions of Microsoft SQL Server can be used with Access as an alternative to the Jet Database Engine. This support started with MSDE (Microsoft SQL Server Desktop Engine), a scaled down version of Microsoft SQL Server , and continues with the SQL Server Express versions of SQL Server and
Microsoft Access is a file server-based database. Unlike client–serverrelational database management systems (RDBMS), Microsoft Access does not implement database triggers, stored procedures, or transaction logging. Access includes table-level triggers and stored procedures built into the ACE data engine. Thus a Client-server database system is not a requirement for using stored procedures or table triggers with Access Tables, queries, forms, reports and macros can now be developed specifically for web based applications in Access Integration with Microsoft SharePoint is also highly improved.
The edition of Microsoft Access introduced a mostly flat design and the ability to install apps from the Office Store, but it did not introduce new features. The theme was partially updated again for , but no dark theme was created for Access.
Access Services and Web database
See also: Web form
ASP.NETweb forms can query a Microsoft Access database, retrieve records and display them on the browser.
SharePoint Server via Access Services allows for Access databases to be published to SharePoint, thus enabling multiple users to interact with the database application from any standards-compliant Web browser. Access Web databases published to SharePoint Server can use standard objects such as tables, queries, forms, macros, and reports. Access Services stores those objects in SharePoint.
Access offers the ability to publish Access web solutions on SharePoint Rather than using SharePoint lists as its data source, Access uses an actual SQL Server database hosted by SharePoint or SQL Azure. This offers a true relational database with referential integrity, scalability, maintainability, and extensibility compared to the SharePoint views Access used. The macro language is enhanced to support more sophisticated programming logic and database level automation.
Import or link sources
Microsoft Access can also import or link directly to data stored in other applications and databases. Microsoft Office Access and newer can import from or link to:
Microsoft Access Runtime
Microsoft offers free runtime versions of Microsoft Access which allow users to run an Access desktop application without needing to purchase or install a retail version of Microsoft Access. This actually allows Access developers to create databases that can be freely distributed to an unlimited number of end-users. These runtime versions of Access and later can be downloaded for free from Microsoft. The runtime versions for Access and earlier were part of the Office Developer Extensions/Toolkit and required a separate purchase.
The runtime version allows users to view, edit and delete data, along with running queries, forms, reports, macros and VBA module code. The runtime version does not allow users to change the design of Microsoft Access tables, queries, forms, reports, macros or module code. The runtime versions are similar to their corresponding full version of Access and usually compatible with earlier versions; for example Access Runtime allows a user to run an Access application made with the version as well as through Due to deprecated features in Access , its runtime version is also unable to support those older features. During development one can simulate the runtime environment from the fully functional version by using the command line option.
Access stores all database tables, queries, forms, reports, macros, and modules in the Access Jet database as a single file.
For query development, Access offers a "Query Designer", a graphical user interface that allows users to build queries without knowledge of structured query language. In the Query Designer, users can "show" the datasources of the query (which can be tables or queries) and select the fields they want returned by clicking and dragging them into the grid. One can set up joins by clicking and dragging fields in tables to fields in other tables. Access allows users to view and manipulate the SQL code if desired. Any Access table, including linked tables from different data sources, can be used in a query.
Access also supports the creation of "pass-through queries". These snippets of SQL code can address external data sources through the use of ODBC connections on the local machine. This enables users to interact with data stored outside the Access program without using linked tables or Jet. Users construct the pass-through queries using the SQL syntax supported by the external data source.
When developing reports (in "Design View") additions or changes to controls cause any linked queries to execute in the background and the designer is forced to wait for records to be returned before being able to make another change. This feature cannot be turned off.
Non-programmers can use the macro feature to automate simple tasks through a series of drop-down selections. Macros allow users to easily chain commands together such as running queries, importing or exporting data, opening and closing forms, previewing and printing reports, etc. Macros support basic logic (IF-conditions) and the ability to call other macros. Macros can also contain sub-macros which are similar to subroutines. In Access , enhanced macros included error-handling and support for temporary variables. Access also introduced embedded macros that are essentially properties of an object's event. This eliminated the need to store macros as individual objects. However, macros were limited in their functionality by a lack of programming loops and advanced coding logic until Access With significant further enhancements introduced in Access , the capabilities of macros became fully comparable to VBA. They made feature rich web-based application deployments practical, via a greatly enhanced Microsoft SharePoint interface and tools, as well as on traditional Windows desktops.
In common with other products in the Microsoft Office suite, the other programming language used in Access is Microsoft VBA. It is similar to Visual Basic (VB6) and code can be stored in modules, classes, and code behind forms and reports. To create a richer, more efficient and maintainable finished product with good error handling, most professional Access applications are developed using the VBA programming language rather than macros, except where web deployment is a business requirement.
To manipulate data in tables and queries in VBA or macros, Microsoft provides two database access libraries of COM components:
- Data Access Objects (DAO) (bit only), which is included in Access and Windows and evolved to ACE in Microsoft Access for the ACCDE database format
- ActiveX Data Objects ActiveX Data Objects (ADO) (both bit and bit versions)
As well as DAO and ADO, developers can also use OLE DB and ODBC for developing native C/C++ programs for Access. For ADPs and the direct manipulation of SQL Server data, ADO is required. DAO is most appropriate for managing data in Access/Jet databases, and the only way to manipulate the complex field types in ACCDB tables.
In the database container or navigation pane in Access and later versions, the system automatically categorizes each object by type (e.g., table, query, macro). Many Access developers use the Leszynski naming convention, though this is not universal; it is a programming convention, not a DBMS-enforced rule. It is particularly helpful in VBA where references to object names may not indicate its data type (e.g. tbl for tables, qry for queries).
Developers deploy Microsoft Access most often for individual and workgroup projects (the Access 97 speed characterization was done for 32 users). Since Access 97, and with Access and , Microsoft Access and hardware have evolved significantly. Databases under 1 GB in size (which can now fit entirely in RAM) and simultaneous users are well within the capabilities of Microsoft Access. Of course, performance depends on the database design and tasks. Disk-intensive work such as complex searching and querying take the most time.
As data from a Microsoft Access database can be cached in RAM, processing speed may substantially improve when there is only a single user or if the data is not changing. In the past, the effect of packet latency on the record-locking system caused Access databases to run slowly on a virtual private network (VPN) or a wide area network (WAN) against a Jet database. As of ,[update] broadband connections have mitigated this issue. Performance can also be enhanced if a continuous connection is maintained to the back-end database throughout the session rather than opening and closing it for each table access.
In July , Microsoft acknowledged an intermittent query performance problem with all versions of Access and Windows 7 and Windows Server R2 due to the nature of resource management being vastly different in newer operating systems. This issue severely affects query performance on both Access and earlier with the Jet Database Engine code, as well as Access and later with the Access Database Engine (ACE). Microsoft has issued hotfixes KB for Access and KB for Access , but will not fix the issue with Jet as it is out of mainstream support.
In earlier versions of Microsoft Access, the ability to distribute applications required the purchase of the Developer Toolkit; in Access , and Access the "Runtime Only" version is offered as a free download, making the distribution of royalty-free applications possible on Windows XP, Vista, 7 and Windows 8.x.
Split database architecture
Microsoft Access applications can adopt a split-database architecture. The single database can be divided into a separate "back-end" file that contains the data tables (shared on a file server) and a "front-end" (containing the application's objects such as queries, forms, reports, macros, and modules). The "front-end" Access application is distributed to each user's desktop and linked to the shared database. Using this approach, each user has a copy of Microsoft Access (or the runtime version) installed on their machine along with their application database. This reduces network traffic since the application is not retrieved for each use. The "front-end" database can still contain local tables for storing a user's settings or temporary data. This split-database design also allows development of the application independent of the data. One disadvantage is that users may make various changes to their own local copy of the application and this makes it hard to manage version control. When a new version is ready, the front-end database is replaced without impacting the data database. Microsoft Access has two built-in utilities, Database Splitter and Linked Table Manager, to facilitate this architecture.
Linked tables in Access use absolute paths rather than relative paths, so the development environment either has to have the same path as the production environment or a "dynamic-linker" routine can be written in VBA.
For very large Access databases, this may have performance issues and a SQL backend should be considered in these circumstances. This is less of an issue if the entire database can fit in the PC's RAM since Access caches data and indexes.
Migration to SQL Server
Main article: Upsizing (database)
To scale Access applications to enterprise or web solutions, one possible technique involves migrating to Microsoft SQL Server or equivalent server database. A client–server design significantly reduces maintenance and increases security, availability, stability, and transaction logging.
Access through Access included a feature called the Upsizing Wizard that allowed users to upgrade their databases to Microsoft SQL Server, an ODBC client–server database. This feature was removed from Access An additional solution, the SQL Server Migration Assistant for Access (SSMA), continues to be available for free download from Microsoft.
A variety of upgrading options are available. After migrating the data and queries to SQL Server, the Access database can be linked to the SQL database. However, certain data types are problematic, most notably "Yes/No". In Microsoft Access there are three states for the Yes/No (True/False) data type: empty, no/false (zero) and yes/true (-1). The corresponding SQL Server data type is binary, with only two states, permissible values, zero and 1. Regardless, SQL Server is still the easiest migration. Retrieving data from linked tables is optimized to just the records needed, but this scenario may operate less efficiently than what would otherwise be optimal for SQL Server. For example, in instances where multi-table joins still require copying the whole table across the network.
In previous versions of Access, including Access , databases can also be converted to Access Data Projects (ADP) which are tied directly to one SQL Server database. This feature was removed from Access ADP's support the ability to directly create and modify SQL Server objects such as tables, views, stored procedures, and SQL Server constraints. The views and stored procedures can significantly reduce the network traffic for multi-table joins. SQL Server supports temporary tables and links to other data sources beyond the single SQL Server database.
Finally, some Access databases are completely replaced by another technology such as ASP.NET or Java once the data is converted. However any migration may dictate major effort since the Access SQL language is a more powerful superset of standard SQL. Further, Access application procedures, whether VBA and macros, are written at a relatively higher level versus the currently available alternatives that are both robust and comprehensive. Note that the Access macro language, allowing an even higher level of abstraction than VBA, was significantly enhanced in Access and again in Access
In many cases, developers build direct web-to-data interfaces using ASP.NET, while keeping major business automation processes, administrative and reporting functions that don't need to be distributed to everyone in Access for information workers to maintain.
While all Access data can migrate to SQL Server directly, some queries cannot migrate successfully. In some situations, you may need to translate VBA functions and user defined functions into TSQL or .NET functions / procedures. Crosstab queries can be migrated to SQL Server using the PIVOT command.
Microsoft Access applications can be made secure by various methods, the most basic being password access control; this is a relatively weak form of protection.
A higher level of protection is the use of workgroup security requiring a user name and password. Users and groups can be specified along with their rights at the object type or individual object level. This can be used to specify people with read-only or data entry rights but may be challenging to specify. A separate workgroup security file contains the settings which can be used to manage multiple databases. Workgroup security is not supported in the Access and Access ACCDB database format, although Access and Access still support it for MDB databases.
Databases can also be encrypted. The ACCDB format offers significantly advanced encryption from previous versions.
Additionally, if the database design needs to be secured to prevent changes, Access databases can be locked/protected (and the source code compiled) by converting the database to a .MDE file. All changes to the VBA project (modules, forms, or reports) need to be made to the original MDB and then reconverted to MDE. In Access and Access , the ACCDB database is converted to an ACCDE file. Some tools are available for unlocking and "decompiling", although certain elements including original VBA comments and formatting are normally irretrievable.
Microsoft Access saves information under the following file formats:
|Access Blank Project Template||.adn|
|Access Database ( and later)||.accdb|
|Access Database Runtime ( and later)||.accdr|
|Access Database Template ( and later)||.accdt|
|Access Add-In ( and later)||.accda|
|Access Workgroup, database for user-level security.||.mdw|
|Protected Access Database, with compiled VBA and macros ( and later)||.accde|
|Windows Shortcut: Access Macro||.mam|
|Windows Shortcut: Access Query||.maq|
|Windows Shortcut: Access Report||.mar|
|Windows Shortcut: Access Table||.mat|
|Windows Shortcut: Access Form||.maf|
|Access lock files (associated with .accdb)||.laccdb|
|Protected Access Data Project (not supported in )||.ade|
|Access Data Project (not supported in )||.adp|
|Access Database ( and earlier)||.mdb|
|Access Database (Pocket Access for Windows CE)||.cdb|
|Access Database, used for addins (Access 2, 95, 97),|
previously used for workgroups (Access 2)
|Access Blank Database Template ( and earlier)||.mdn|
|Access (SQL Server) detached database ()||.mdf|
|Protected Access Database, with compiled VBA and macros ( and earlier)||.mde|
|Access lock files (associated with .mdb)||.ldb|
|Release Date||Jet version||Supported OS||Office suite version|
|Windows x||Office Pro|
|August 24,||Windows 95||Office 95 Professional|
|January 16,||Windows 95, Windows NT SP5, Windows NT SP2||Office 97 Professional and Developer|
|June 7,||SP1||Windows 95, Windows NT , Windows 98, Windows ||Office Professional, Premium and Developer|
|May 31,||Windows NT SP6, Windows 98, Windows , Windows Me||Office XP Professional and Developer|
|November 27,||Windows SP3 or later, Windows XP, Windows Vista, Windows 7||Office Professional and Professional Enterprise|
|January 27,||Windows XP SP2, Windows Server SP1, or newer operating system||Office Professional, Professional Plus, Ultimate and Enterprise|
|July 15,||Windows XP SP3, Windows Server SP2, Windows Server R2, Windows Vista SP1, Windows Server , Windows 7, Windows Server R2, Windows Server , Windows 8||Office Professional, Professional Academic and Professional Plus|
|January 29,||Windows 7, Windows Server R2, Windows Server , Windows 8, Windows 10||Office Professional and Professional Plus|
|September 22,||16||Windows 7, Windows 8, Windows , Windows 10||Office Professional and Professional Plus|
|September 24,||Windows 10||Office Professional and Professional Plus|
There are no Access versions between and because the Office 95 version was launched with Word 7. All of the Office 95 products have OLE 2 capabilities, and Access 7 shows that it was compatible with Word 7.
Version number 13 was skipped.
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MS Access Functions
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