You use update queries in Access databases to add, change, or delete the information in an existing record. You can think of update queries as a powerful form of the. Creating an MS Access Unbound Single Form. Create the SQL Server table to use in SSMS and INSERT some data from a view or other table. Microsoft Access Update Query examples, SQL Syntax and errors with update queries. SQL Server Performance Performance Tuning Tips for Using Microsoft Access and SQL Server Together. If you are interested in the fastest performance, don’t use Access as a front- end to a SQL Server database. While Access is relatively easy to learn and fast to develop in, its performance is poor when compared to other front- end options. But if you like to develop in Access, or don’t have any choice, then follow the tips on this page to help boost your application’s performance. Microsoft Access Query Tips and Techniques (SQL and VBA) by Luke Chung, President of FMS, Inc. This paper is featured on: Overview. Microsoft Access is the most. ![]() ![]() Updated 2- 2. 0- 2. When you write a query in Access that needs to run against a SQL Server database, Access will locally evaluate the query, looking for any clauses or expressions that cannot be run on SQL Server, and those that can. It will do its best to run as much of the query, if not the entire query, on SQL Server rather than locally. This is because SQL Server can run the queries much faster than Access can. If Access cannot run the entire query on SQL Server, it will run as much as possible on it, and when it retrieves the results set from SQL Server, it will then complete the query locally. In order to speed up Access queries, you should try to write Access queries that will run entirely, or as much as possible, on SQL Server, instead of locally on Access. While the list is too long to include here, some of the query clauses and expressions that can run on Access but not on SQL Server, and ones you should try to avoid, include domain aggregate function, financial functions, and user- defined functions. Updated 2- 2. 0- 2. When you design forms that include data from a SQL Server, try to avoid downloading data that the user doesn’t immediately need. This will reduce network traffic, reduce the load on the server, and speed overall performance. Some ways to reduce the amount of the data you download to a form include: Try to avoid opening large Recordset objects and then navigating through them using one of the Find methods. Instead, use a filter or query to limit the size of the recordset in the first place. Only retrieve fields from records that you actually need on the form. Avoid using bound controls on your form. Each bound control creates a separate query that must be sent to and run on SQL Server. If the user doesn’t need to view all the data from a record in a SQL Server database at the same time, use two forms. The first form will include the most important data and it will be retrieved from SQL Server based on a query to SELECT only the data that needs to be on this first form. If the user needs the rest of the data, then the user can click on a button to bring up the second form. The data for the second form is only requested if the user clicks on the button for the second form. This way, only the data that is needed for the current form is ever requested from SQL Server. Don’t display Memo or OLE object fields on a form unless the user specifically requests this information by clicking on a button. The advantage of this technique is that Access does not retrieve Memo or OLE object fields from SQL Server until the fields themselves are displayed on the screen. Updated 2- 2. 0- 2. When displaying SQL Server data on a form, Access allows you to create either a dynaset or a snapshot Recordset object. If you don’t need to update the data displayed on the form, and if the Recordset has less than 5. Recordset will be faster than the dynaset Recordset. But if the Recordset is over 5. Memo or OLE Object fields, then the dynaset Recordset object is faster. Updated 2- 2. 0- 2. If possible, avoid using subforms in your Access forms. Subforms require at least two queries to be issued to SQL Server, and require more overhead. Instead, use a query to join the tables you need and display the results in the form. This only requires one query to be sent to SQL Server and has less overhead. Most columns from multiple- table tables can have data inserted or updated into them, so subforms can often be avoided. Updated 2- 2. 0- 2. One way to increase performance of DELETEs or UPDATEs made by your Access front- end to a SQL Server backend is to ensure that the table on SQL Server has a timestamp column. ![]() If a table does have a timestamp column, then when Access DELETEs or UPDATEs a row, Access will automatically check the timestamp column to see if it has changed during the time that the transaction begun and the current time that the deletion or update is being made. If the timestamp column has changed, then the DELETE or UPDATE will be aborted. If a timestamp column does not exist in the table, then Access will have to compare all the field values when the transaction begun to their current value to determine if there were any changes. This is much slower for Access to perform than checking the timestamp column. Updated 2- 2. 0- 2. To help improve scalability and performance of INSERTs, UPDATEs, and DELETEs, try to include related INSERTs, UPDATEs, and DELETEs together in formal transactions. For example, if a particular transaction includes multiple UPDATEs, then these will all be submitted to SQL Server as one single batch, instead of many separate batches. This reduces network traffic and server overhead. But like any transactions, they should always be made as short as possible to minimize locking on the SQL Server tables. Updated 2- 2. 0- 2. Link Access Applications to SQL Server - Azure SQL DBIf you want to use your existing Access applications with SQL Server, you can link your original Access tables to the migrated SQL Server or SQL Azure tables. Linking modifies your Access database so that your queries, forms, reports, and data access pages use the data in the SQL Server or SQL Azure database instead of the data in your Access database. Note. Your Access tables remain in Access, but are not updated together with SQL Server or SQL Azure updates. After you link the tables and verify functionality, you might want to delete your Access tables. Linking Access and SQL Server tables. When you link an Access table to a SQL Server or SQL Azure table, the Jet database engine stores connection information and table metadata, but the data is stored in SQL Server or SQL Azure. This linking allows your Access applications operate against the Access tables even though the actual tables and data are in SQL Server or SQL Azure. Note. If you use SQL Server Authentication, your password is stored in clear text on the linked Access tables. We recommend using Windows Authentication. To link tables. In Access Metadata Explorer, select the tables that you want to link. Right- click Tables, and then select Link. SQL Server Migration Assistant (SSMA) for Access backs up the original Access table and creates a linked table. After you link the tables, the tables in SSMA appear with a small link icon. In Access, the tables appear with a "linked" icon, which is a globe with an arrow pointing to it. When you open a table in Access, the data is retrieved using a keyset cursor. As a result, for large tables, all the data is not retrieved at one time. However, as you browse through the table, Access retrieves additional data as necessary. Unlinking Access tables. When you unlink an Access table from a SQL Server or SQL Azure table, SSMA restores the original Access table and its data. To unlink tables. In Access Metadata Explorer, select the tables that you want to unlink. Right- click Tables, and then select Unlink. Linking tables to a different server. If you have linked the Access tables to one SQL Server instance and you later want to change the links to another instance, you must relink the tables. To link tables to a different server. In Access Metadata Explorer, select the tables that you want to unlink. Right- click Tables and then select Unlink. Click the Reconnect to SQL Server button. Connect to the instance of SQL Server or SQL Azure to which you want to link the Access tables. In Access Metadata Explorer, select the tables that you want to link. Right- click Tables, and then select Link. Updating linked tables. If the SQL Server or SQL Azure table definitions are altered, you can unlink and then re- link the tables in SSMA by using the procedures shown previously in this topic. You can also update the tables by using Access. To update linked tables by using Access. Open the Access database. In the Objects list, click Tables. Right- click a linked table, and then select Linked Table Manager. Select the check box next to each linked table that you want to update, and then click OK. Possible post- migration issues. The following sections list issues that might occur in existing Access applications after you migrate databases from Access to SQL Server or SQL Azure and then link the tables, together with the causes and the resolutions. Slow performance with linked tables. Cause: Some queries might be slow after upsizing for the following reasons: The application depends on functions that do not exist in SQL Server or SQL Azure, which causes Jet to pull down tables locally to run a SELECT query. Queries that update or delete many rows are sent by Jet as a parameterized query for each row. Resolution: Convert the slow- running queries to pass- through queries, stored procedures, or views. Converting to pass- through queries has the following issues: Pass- through queries cannot be modified. Modifying the query result or adding new records must be done in an alternative way, such as by having explicit Modify or Add buttons on your form that is bound to the query. Some queries require user input, but pass- through queries do not support user input. User input can be obtained by Visual Basic for Applications (VBA) code that prompts for parameters, or by a form that is used as an input control. In both cases, the VBA code submits the query with the user input to the server. Auto- increment columns are not updated until the record is updated. Cause: After calling Record. Set. Add. New in Jet, the auto increment column is available before the record is updated. This is not true in SQL Server or SQL Azure. The new value of the identity column new value is available only after saving the new record. Resolution: Run the following Visual Basic for Applications (VBA) code before accessing the identity field: Recordset. Update. Recordset. Move 0. Recordset. Last. Modified. New records are not available. Cause: When you add a record to a SQL Server or SQL Azure table by using VBA, if the table's unique index field has a default value and you do not assign a value to that field, the new record does not appear until you reopen the table in SQL Server or SQL Azure. If you try to obtain a value from the new record, you receive the following error message: Run- time error '3. Record is deleted. Resolution: When you open the SQL Server or SQL Azure table by using VBA code, include the db. See. Changes option, as in the following example: Set rs = db. Open. Recordset("Test. Table", db. Open. Dynaset, db. See. Changes)After migration, some queries will not allow the user to add a new record. Cause: If a query does not include all columns that are included in a unique index, you cannot add new values by using the query. Resolution: Ensure that all columns included in at least one unique index are part of the query. You cannot modify a linked table schema with Access. Cause: After migrating data and linking tables, the user cannot modify the schema of a table in Access. Resolution: Modify the table schema by using SQL Server Management Studio, and then update the link in Access. Hyperlink functionality is lost after migrating data. Cause: After migrating data, hyperlinks in columns lose their functionality and become simple nvarchar(max) columns. Resolution: None. Some SQL Server data types are not supported by Access. Cause: If you later update your SQL Server or SQL Azure tables to contain data types that are not supported by Access, you cannot open the table in Access. Resolution: You can define an Access query that returns only those rows with supported data types. See also. Migrating Access Databases to SQL Server.
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October 2017
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