About the Series …
This article continues the series, MS Access for the
Business Environment. The primary focus of this series is an
examination of business uses for the MS Access relational database management
system. The series is designed to provide guidance in the practical application
of data and database concepts to meet specific needs in the business world.
While the majority of the procedures I demonstrate will be undertaken with MS
Access 2002, many of the concepts that we explore in the series will apply
to other versions of MS Access.
For more information on the series, as well as the hardware
/ software requirements to prepare for the tutorials we will undertake, please
see Tutorial
1: Create a Calculated Field with the
Expression Builder.
Introduction to this
Tutorial
While we have considered basic queries in past lessons,
particularly as a basis for reporting and other topics, most of the queries we
have encountered could have been assembled without writing "direct SQL."
That is, they might have just as easily been constructed using the Design
view, or perhaps even with the Query Builder, behind both of which MS Access
constructs the SQL for us. There are, however, many cases where the SQL we
need to handle real-world requirements cannot be assembled adequately with the Query
Builder, or even within Design view. The MS Access documentation
refers to several groups of these as "SQL-specific" queries,
including pass-through, data definition, and union queries.
Subqueries are another group that requires special
attention, and, while we can construct many of them within the query design
grid, I find that situations requiring subqueries, as well as other
sophisticated solutions, are best handled through the use of direct SQL. One
of the best things about the SQL view in MS Access is that it allows us
to "flip" from a query displayed / under construction in one of the
two graphical modes to the actual SQL behind the scenes – and thus an excellent
learning experience can be accessed by a simple click of the view button, which
allows us to shift between Design, Datasheet, and SQL views
within any query, and at any time, to suit our needs.
The objective of this lesson is
to introduce subqueries within the context of MS Access, and to explore the creation
and use of SQL subqueries to render a result dataset that meets an illustrative
business need. To accomplish this, we will introduce the subquery, discussing
its syntax in general as a part of overviewing its general use. Along with an
introduction to the basic subquery, this lesson will include:
- an examination of the syntax surrounding the use of the subquery;
-
an illustrative, hands-on example of the use of a subquery in a multi-step
practice exercise; -
a brief discussion of the results datasets that we obtain in each
step of the practice example.
We will use the Northwind sample database that
installs with MS Access for purposes of this lesson, in an attempt to make the
lesson useful to virtually anyone who has access to MS Access.
