When you want to either quickly delete a lot of data or delete a set of data on a regular basis in an Access desktop database, a delete or an update query might be useful because the queries make it possible to specify criteria to quickly find and delete the data. Using a query can also be a timesaver because you can reuse a saved query.
:Â Before you delete any data or run a delete query, make sure that you have a backup of your Access desktop database.
If you want to only delete a few records, you don’t need a query. Just open the table in Datasheet view, select the fields (columns) or records (rows) that you want to delete, and then press DELETE.
:Â The information in this article is intended for use only with desktop databases. You cannot use delete or update queries in Access web apps.
In this article
Choosing a query type
You can use either an update query or a delete query to delete data from your database. Select a query based on the details in the following table:
|
Type of query |
When to use it |
Results |
|---|---|---|
|
Use a delete query |
To remove entire records (rows) from a table or from two related tables simultaneously. :Â If the records reside on the "one" side of a one-to-many relationship, you might need to change the relationship before you run the delete query. See the section on deleting data from related tables. |
Delete queries remove all the data in each field, including the key value that makes a record unique |
|
Use an update query |
To delete individual field values from a table. |
Makes it easier to delete values by updating the existing values to either a null value (that is, no data) or a zero-length string (a pair of double quotation marks with no space between them). |
Things to verify before you use a query to delete any data
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Make sure that the file is not a read-only file:
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Right-click Start and click Open Windows Explorer.
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Right-click the database file and click Properties.
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See if the Read-only attribute is selected.
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Verify that you have the necessary permissions to delete records from the database. If you are not sure, contact your system administrator or the database designer.
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Make sure that you have enabled content in the database. By default, Access blocks all action queries (delete, update, and make-table queries) unless you first trust the database. For information about trusting a database, see the section Stop Disabled Mode from blocking a query.
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Ask other users of the database to close all tables, forms, queries, and reports that use the data that you want to delete. This helps avoid lock violations.
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Before you edit or delete records, making a backup copy of the database is a good idea in case you want to reverse your changes.
:Â If a large number of users connect to the database, you might need to close the database and then reopen it in Exclusive mode.
To open a database in Exclusive mode
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Click File tab > Open.
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Browse to and point to select the database, click the arrow next to the Open button, and then click Open Exclusive.
Back up the database
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Click the File tab, point to Save As.
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Click Save Database As, click Back Up Database. Access closes the original file, creates a backup, and then reopens the original file.
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Click Save As and specify a name and location for the backup copy, and click Save.
:Â If you are using a read-only or a database created in the previous version of Access, you might get a message that it is not possible to create a back-up of the database.
To revert to a backup, close and rename the original file so that the backup copy can use the name of the original version. Assign the name of the original version to the backup copy, and open the renamed backup copy in Access.
Using a delete query
To create a delete query, click the Create tab, in the Queries group, click Query Design. Double-click each table from which you want to delete records, and then click Close.
The table appears as a window in the upper section of the query design grid. From the list of fields, double-click the asterisk (*) to add all of the fields in the table to the design grid.
Using a specific criteria in a delete query
:Â Use criteria to return only the records that you want to delete. Otherwise, the delete query removes every record in the table.
Double-click the field that you want to specify as the criteria for deletion, enter one the criteria in the Criteria row of the query designer, and then clear the Show check box for each criteria field.
An example of when you might want to use this option: Suppose you want to remove all of the pending orders for a customer. To find just those records, you’d add the Customer ID and Order Date fields to the query design grid, and then you enter the ID number of the customer, and the date on which that customer's orders became invalid.
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On the Design tab, click View > Datasheet View.
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Verify that the query returns the records that you want to delete, and then press CTRL+S to save the query.
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To run the query, double-click the query in the Navigation Pane.
Using an update query
:Â You cannot use the update query option in an Access web app.
This section explains how to use an update query to delete individual fields from tables. Remember that running an update query to delete data will change the existing values to either NULL or a zero-length string (a pair of double quotation marks with no space in between), depending on the criteria that you specify.
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Click the Create tab and in the Queries group, click Query Design.
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Select the table which has the data you want to delete (if the table is related, select the table on the "one" side of the relationship), click Add, and then click Close.
The table appears as a window in the upper section of the query design grid. The window lists all of the fields in the selected table.
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Double-click the asterisk (*) to add all of the fields in the table to the design grid. Adding all the table fields enables the delete query to remove entire records (rows) from the table.
Optionally, you can enter criteria for one or more fields in the Criteria row of the designer, and then clear the Show check box for each criteria field. For more information about using criteria, see the Sample criteria for select queries table.
:Â You use criteria to return only the records that you want to change. Otherwise, the update query sets to NULL every record in each of the fields in your query.
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On the Design tab, in the Results group, click View, and then click Datasheet View.
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Verify that the query returns the records that you want to set to NULL or a zero-length string (a pair of double-quotation marks with no space between them ("").
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As needed, repeat steps 3 to 5 and change the fields or criteria until the query returns only the data that you want to delete, and then press CTRL+S to save the query.
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To run the query, double-click the query in the Navigation Pane.
Additional Information
Deleting data from related tables
If you want to delete data from several related tables, you must enable the Referential Integrity and Cascade Delete Related Records options for each relationship. This allows your query to delete data from the tables on the "one" and "many" sides of the relationship. Preparing to deleted related data requires verification of the following:
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Determine which records reside on the "one" side of the relationship and which reside on the "many" side.
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If you need to delete records on the "one" side of the relationship and the related records on the "many" side, you enable a set of rules called Referential Integrity, and you enable cascading deletes. Steps in this section explain Referential Integrity, and how to perform both tasks.
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If you need to delete records only on the "one" side of the relationship, you first delete that relationship, and then delete the data.
If you need to remove data only on the "many" side of the relationship, you can create and run your delete query without having to change the relationship.
To find out which records reside on the "one" and "many" sides of a relationship, on the Database Tools tab, in the Relationships group, click Relationships. The Relationships tab displays the tables in your database and the relationships. Each relationship is depicted as a line that connects tables between fields.
The following figure shows a typical relationship. Most, if not all, of the relationships in a database have a "one" side and a "many" side. The relationship diagram denotes the "one" side with the numeral one (1) and the "many" side with the infinity (∞) symbol.
When you delete records on the "one" side of the relationship, you also delete all of the related records on the "many" side of the relationship. However, when you delete records on the "many" side of a relationship, you typically don't delete records on the "one" side.
Also, Access automatically enforces a set of rules called referential integrity. These rules ensure that the foreign keys in a database contain the correct values. A foreign key is a column whose values match the values in the primary key column of another table.
Edit the relationship
Follow these steps only when you need to delete data on the "one" and "many" sides of a relationship.
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On the Database Tools tab, in the Relationships group, click Relationships.
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Right-click the relationship (the line) connecting the tables involved in the deletion operation, and then click Edit Relationship on the shortcut menu.
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In the Edit Relationships dialog box, ensure that the Enforce Referential Integrity check box is selected.
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Select the Cascade Delete Related Records check box.
:Â Until you disable this property again, deleting a record on the "one" side of the relationship will delete all of the related records on the "many" side of the relationship.
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Click OK, close the Relationships pane, and then go on to the next set of steps.
Delete a relationship
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If you haven't done so already, open the Relationships pane.
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On the Database Tools tab, in the Relationships group, click Relationships.
Make a note of the fields involved in the relationship so that you can restore the relationship after you delete your data.
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Right-click the relationship (the line) connecting the tables involved in the deletion operation, and then click Delete on the shortcut menu.
:Â To restore the relationship, follow the previous steps to open the Relationships pane, and then drag the primary key field from the "one" table and drop it on the foreign key field of the "many" table. The Edit Relationship dialog box appears. If the old relationship enforced referential integrity, select Enforce Referential Integrity, and then click Create. Otherwise, just click Create.
Sample criteria for select queries
The following table lists some sample criteria that you can use in select queries when you want to make sure that you delete only the data that you want deleted. Some of these examples use wildcard characters.
|
Criteria |
Effect |
|---|---|
|
> 234 |
Returns all numbers greater than 234. To find all numbers less than 234, use < 234. |
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>= "Cajhen" |
Returns all records from Cajhen through the end of the alphabet. |
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Between #2/2/2010# And #12/1/2010# |
Returns dates from 2-Feb-2010 through 1-Dec-2010 (ANSI-89). If your database uses the ANSI-92 wildcard characters, use single quotation marks (') instead of pound signs (#). Example: Between '2/2/2010' And '12/1/2010'. |
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Not "Germany" |
Finds all records where the exact contents of the field are not exactly equal to "Germany." The criterion will return records that contain characters in addition to "Germany," such as "Germany (euro)" or "Europe (Germany)". |
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Not "T*" |
Finds all records except those beginning with T. If your database uses the ANSI-92 wildcard character set, use the percent sign (%) instead of the asterisk (*). |
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Not "*t" |
Finds all records that do not end with t. If your database uses the ANSI-92 wildcard character set, use the percent sign (%) instead of the asterisk (*). |
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In(Canada,UK) |
In a list, finds all records containing Canada or UK. |
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Like "[A-D]*" |
In a Text field, finds all records that start with the letters A through D. If your database uses the ANSI-92 wildcard character set, use the percent sign (%) instead of the asterisk (*). |
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Like "*ar*" |
Finds all records that include the letter sequence "ar". If your database uses the ANSI-92 wildcard character set, use the percent sign (%) instead of the asterisk (*). |
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Like "Maison Dewe?" |
Finds all records that begin with "Maison" and contain a 5-letter second string in which the first 4 letters are "Dewe" and the last letter is unknown. If your database uses the ANSI-92 wildcard character set, use the underscore (_) instead of the question mark (?). |
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#2/2/2010# |
Finds all records for February 2, 2010. If your database uses the ANSI-92 wildcard character set, surround the date with single quotation marks instead of pound signs ('2/2/2010'). |
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< Date() - 30 |
Uses the Date function to return all dates more than 30 days old. |
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Date() |
Uses the Date function to return all records containing today's date. |
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Between Date() And DateAdd("M", 3, Date()) |
Uses the Date and the DateAdd functions to return all records between today's date and three months from today's date. |
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Is Null |
Returns all records that contain a null (blank or undefined) value. |
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Is Not Null |
Returns all records that contain any value (that are not null). |
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"" |
Returns all records that contain a zero-length string. You use zero-length strings when you need to add a value to a required field, but you don't yet know what the actual value is. For example, a field might require a fax number, but some of your customers might not have fax machines. In that case, instead of entering a number, you enter a pair of double quotation marks with no space between them (""). |
Troubleshooting tips
Why am I seeing this error message, and how do I fix it?
If you build a delete query by using multiple tables and the query's Unique Records property is set to No, Access displays the error message; Could not delete from the specified tables when you run the query.
To fix this problem, set the query's Unique Records property to Yes.
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Open the delete query in Design view.
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If the query property sheet is not open, press F4 to open it.
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Click the query designer to show the query properties (rather than the field properties).
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In the query property sheet, locate the Unique Records property, and set it to Yes.
Stop Disabled Mode from blocking a query
By default, if you open a desktop database that you have not chosen to trust or that does not reside in a trusted location, Access blocks all action queries from running.
If you try to run an action query and it seems like nothing happens, check the Access status bar for the following message:
This action or event has been blocked by Disabled Mode.
When you see that message, take the following step to enable the blocked content:
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On the Security Warning Message Bar, click Enable Content, and run your query again.
