Microsoft Accesss 2010 : Enhancing the Queries That You Build - Creating and Running Action Queries (part 1) - Creating and Running Update Queries

With Action queries, you can easily modify data without writing any code. In fact, using Action queries is often a more efficient method of modifying data than using code. Four types of Action queries are available: Update, Delete, Append, and Make Table. You use Update queries to modify data in a table, Delete queries to remove records from a table, Append queries to add records to an existing table, and Make Table queries to create an entirely new table. The sections that follow explain these query types and their appropriate uses.

Creating and Running Update Queries

You use Update queries to modify all records or any records that meet specific criteria. You can use an Update query to modify the data in one field or several fields (or even tables) at one time. For example, you could create a query that increases the salary of everyone in California by 10%. As mentioned previously, using Action queries, including Update queries, is usually more efficient than performing the same task with Visual Basic for Applications (VBA) code, so you can consider Update queries a respectable way to modify table data.

Build an Update Query

To build an Update query, follow these steps:

1.	Select Query Design from the Queries group on the Create tab of the Ribbon. The Show Table dialog box appears.
2.	In the Show Table dialog box, select the tables or queries that will participate in the Update query and click Add. Click Close when you’re ready to continue.
3.	To let Access know you’re building an Update query, select Update from the Query Type group on the Design tab of the Ribbon.
4.	Add to the query fields that either you will use for criteria or Access will update as a result of the query. In Figure 1, Ship State/Province is included on the query grid because we will use it as a criterion for the update. Shipping Fee is included because it’s the field that Access will update. Figure 1. An Update query that increases DefaultRate for all clients in California.
5.	Add any further criteria, if you want. In Figure 1, the criterion for Ship State/Province is CA.
6.	Add the appropriate Update expression. The example illustrated in Figure 1 increases DefaultRate by 10%.
7.	Click Run in the Results group on the Design tab of the Ribbon. The message box shown in Figure 2 appears. Click Yes to continue. Access updates all records that meet the selected criteria.

You should name Access Update queries with the prefix qupd. In fact, you should give each type of Action query a prefix indicating what type of query it is. This makes your application easier to maintain, and makes your code more readable, and renders your code self-documenting. Table 1 lists all the commonly accepted prefixes for Action queries.

Access stores all queries as Structured Query Language (SQL) statements. You can display the SQL for a query by selecting SQL View from the View drop-down list on the toolbar. The SQL behind an Access Update query looks like this:

UPDATE tblClients SET tblClients._
    DefaultRate = [DefaultRate]*1.1
     WHERE (((tblClients.StateProvince)="CA"));

You cannot reverse the actions taken by an Update query or by any Action queries. You must therefore exercise extreme caution when running any Action query.