Download Tutorial 8

Tutorial 8
Advanced Queries
Notes
 Switch to new database!
 Tutorial.08 folder
 Only Session 8.1 and 8.2
Create a crosstab query
 A crosstab query performs aggregate function
(arithmetic operations) calculations on the
values of one database field and displays the
results in a spreadsheet format.
 Possible functions include

average, count, first field value, last field
value, etc.
 Crosstab Query Wizard will walk you through
creating a crosstab query.
A select query versus
a crosstab query
This figure shows a Select query
and a crosstab query. These two
queries are based on the same data.
In this case the crosstab query
is using the Sum function to
summarize the potential
income for each country`.
However, notice that the
crosstab query data is
much more summarized
than the select query data.
Crosstab query aggregate functions
The figure below shows the aggregate functions that can be used in a crosstab query.
The Crosstab Query Wizard steps
1. Select the table or query upon which you
want to create the crosstab query.
2. Select fields to use as row headings.
3. Select fields to use as column headings.
4. Select the field that will be calculated upon
and what calculation is to be performed.
The final Crosstab Query Wizard
dialog box
This figure shows the final Crosstab Query Wizard dialog box where you select the
field to be used for the calculation, and which type of calculation to perform.
Other types of queries
 Find duplicates
 a select query that locates duplicate records in
a table or query
 Find unmatched
 returns a datasheet for all records that do not
have a matching record in the related table
 Top values
 Returns the top number top percentage of
records

E.g. top 10 or top 25%
Action queries
 Queries that make changes to the data in the
underlying table(s).
 Action queries can:




Create a new table (make-table query)
Add records to a table (append query)
Delete records from a table (delete query)
Update the data in a table (update query)
Action query considerations
 These queries change the underlying tables
permanently! Be very careful!!!
 Always create a select query to test it out first


You can then view the results and determine if
these are the records you want to alter.
When you are sure the query is right, run it as
an action query.
Many-to-many Relationships
Between Tables
 A many-to-many relationship exists between tables
when the tables involved have multiple matches in
each of the tables.
 For example, if you have a table containing
student data and another table containing course
data, you could say that this is a (M:N) relationship
because a student can take many courses and a
course can have many students
 Many-to-many relationships require a third table that
will “link” the two tables together in a one-to-many
relationship.
A many-to-many relationship
In the figure below, you see an illustration of a many-to-many relationship.
Note that the Job table is used to join the Position table and the Student table.
The Job table contains
a PositionID and a
StudentID for each
position that a students
holds. In this case, a
student can have more
than one position and a
position can be held by
more than one student.
A query datasheet for a
many-to-many relationship
Once you have created the third table (the table that joins the two tables in a
many-to-many relationship) you can create a query based on all three tables.
The following figure show a query datasheet based on the three tables.