Download CHAPTER 6: ADVANCED DATABASE FEATURES

Chapter 6
Advanced Database Features
Overview
Chapter 6 introduces advanced database skills that will enhance the student’s ability to create
more intricate and organized output. The integration of many SQL commands such as aggregate
functions, as well as the Group/Order By attribute, will help the students to create more
structured and useful views of data. Within a group of queries that may be interdependent, if not
all queries are able to successfully update the database; the <cftransaction> tag can be used to
prevent any of the changes from being committed to the database.
Adding to the repertoire of building modular applications, the chapter continues by visiting
stored procedures in both server based database programs as well as creating and using stored
procedures in file based applications such as MS Access. Creation of dynamic SQL statements
is demonstrated in an example that allows the user to enter the criteria which is subsequently
used within a query to return records matching the value that was specified. The final part of the
chapter explains when and how to use the date conversion functions such as CreateODBCDate
so that the expected format will be used when maintaining date values in a database.
Teaching Tips and Strategies
At this point, the students will have the skills required to create a complete database maintenance
application that will allow them to practice creating dynamic SQL, setting up datasources, and
reinforce skills learned in previous chapters. Using either a simple database that you create, or a
database the students create that will have one table to contain information such as databases or a
collection of some sort – CDs or Books for example.
Have the students create the following templates:
 Main Template – lists records from a table (Book title for example)
o Next to each record, create links for editing and deleting the record. You will have to
send a URL parameter containing the key field value to the action page so that your
query can modify or delete only the corresponding record as well as a URL variable
to specify the action requested (“Edit” or “Delete”).
o Be sure to create an Add link to this page as well which will not send any URL
parameters.
 Add/Edit/Delete Form Template
o If no URL parameters are sent, create empty local variables for each of the form
fields (this means the user is adding a new record).
o If Edit or Delete is specified in the URL parameter, run a query to retrieve the
corresponding record using dynamic SQL and set local variables to contain these
values.
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o Be sure to create a local variable in each of the three cases that stores the button text
for the submission of the form. You will want to make sure to make each one unique
so that you can differentiate what action should be performed on the action page.
o Create the form using the local variables in the Value parameter of the form field.
o Create a hidden input field that stores the primary key sent from the main page if edit
or delete.
 Action Template
o Retrieve the value of the submit button created on the form page and determine if the
value is “Add”, “Edit”, or “Delete”
o If Add – create SQL INSERT to insert form values to database
o If Edit – create SQL UPDATE to update values for the corresponding record in the
database
o If Delete – create SQL DELETE to delete the corresponding record in the database
Once the appropriate action is completed, have the students browse the main page again to view
changes to the data.
Lecture Notes
I. SQL Aggregate Functions
A. Count – returns the number of rows in a column
B. Min – returns the smallest value
C. Max – returns the largest value
D. Avg – returns the average of values in a column
E. Sum – adds all the values in a column
F. Use an alias to access the results of an aggregate function
II. SQL Group By/Order By commands
A. Group By sorts the results on one or more fields in many server-based database
systems. Order By gives the same result in MS Access.
B. In MS Access, Group By works only in conjunction with an aggregate function.
III. Transaction Processing and Database Security
A. The <cftransaction> tag is used in ColdFusion to:
1. Keep the database from being updated unless all queries can be completed.
2. Provide a locking mechanism for the records in the table.
B. <cftransaction> uses the following attributes:
1. Action
a) Begin – marks the starting point
b) Commit – commits pending queries
c) RollBack – rolls back pending queries
2. Isolation
a) Serializable – exclusive locking allowed
b) Repeatable Read – allows ability to insert data by other SQL
statements
c) Read Committed – both read and insert data
d) Read Uncommitted – readers can see changes prior to commit
IV. Stored Procedures – a query created previously and called when necessary.
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A. Database access is minimized which speeds up processing time.
B. Allows the same query to be used in many different applications.
C. Promotes Modular and Team programming.
V. Dynamic SQL
A. Create parameter-based queries by allowing the user to supply the value that will be
used as the criterion value in the query.
VI. Working with Dates
A. CreateODBCDateTime() ColdFusion function may be used to convert dates entered
by the user into a format that is understand by the database.
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Review Questions
Answers:
1.
These SQL functions are performed on a column in a table and the result returned is a single
value for each function. The method of using Aliases for field names or Column names
can come in very handy especially when the field names in question are cryptic or lengthy.
Once you create an alias, you will be able to use the alias instead of the original field name.
For example, in your output tag you could say
<cfoutput #minPrice#>
where the alias minPrice stands for the minimum value in the column UnitPrice
2.
Aggregate functions are performed on a column.
3.
Any function returns one result.
4.
The SQL Group By command allows you to organize and categorize records in the table
based on a certain criterion (value in a column). Grouping enables the presentation of data
returned by the query in an organized manner. Group By works well with server-based
database systems like ORACLE or SQL SERVER
5.
Transaction processing is the process of grouping together a set of queries sent to the
database via the server. This process serves two main purposes:
1. To ensure that a group of queries succeed or fail in totality. The benefit here is that the
database will not be altered until all steps required to be completed are completed, thus
maintaining the integrity of the database.
2. To provide a mechanism for locking the records of the table when the table is being
used, thus not allowing multiple users to manipulate and modify the data at the same
time.
6.
CFTRANSACTION tag has two optional attributes:
1. Action (this attribute has three options)
a. Begin (is the default value, marks the starting point of the block of code to be
executed in sequence)
b. Commit (commits the set of pending queries or code segments to be executed)
c. RollBack (restores the state that existed before the set of pending queries or
code segments were executed)
2. Isolation (this attribute supports four levels)
a. Serializable (highest level – allows exclusive locking, nobody other than the
current user can modify the data being read)
b. Repeatable Read (allows ability to insert data by other SQL statements)
c. Read Committed (allows ability to both read and insert data)
d. Read Uncommitted (similar to SQL commit, but readers can see the changes
prior to commit)
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7.
Chapter 6: Advanced Database Features
ColdFusion cannot directly lock a database, but it provides a method via the
CFTRANSACTION’s isolation attribute. This attribute supports four levels:
1. Serializable (highest level – allows exclusive locking, nobody other than the
current user can modify the data being read)
2. Repeatable Read (allows ability to insert data by other SQL statements)
3. Read Committed (allows ability to both read and insert data)
4. Read Uncommitted (similar to SQL commit, but readers can see the changes
prior to commit)
8.
No, All ColdFusion tags within a transaction must use the same datasource.
9.
The Cascade DELETE option must be enabled in MS Access on the relationships between
tables to ensure that all related records in different tables do get deleted when you issue a
DELETE SQL command via ColdFusion.
10. A Stored Procedure is just a query created earlier and called when necessary. Stored
procedures have a number of benefits such as:
1. Avoid traffic via the network and provide speed of execution: since the query is
already built and saved in the database, database access is minimized, thus the
processing time speeds up.
2. Enables Reuse: once created, stored procedures allow for the concept of reuse which is
a very crucial component of efficient and good programming.
3. Promote Modular and Team programming: since stored procedures can be thought of
as individual blocks, they can be developed as modules where each module can be
developed by different members of the team thus benefiting from the advantages of
modular and team programming concepts.
11. The SQL command sent to the server is said to be dynamic because the database will not
know the SQL statement being sent to it until runtime. This is an important concept in all
web based programming technologies such as ColdFusion, ASP, PHP etc. because these
technologies allow the user to send queries to the sever on the fly and get the results on the
browser.
12. An electronic shopping cart is an excellent example because the application must check the
quantity in stock each time a user requests a product by sending a query to the database, and
depending on the result returned by the query, the customer is allowed to proceed or gets a
message “out of stock.”
True/False
Answers:
1.
False
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2.
False
3.
True
4.
True
5.
True
Chapter 6: Advanced Database Features
Programming Exercises
Answers:
1.
See CH06_EX01A-SOL.CFM for the action page and CH06_EX01F-SOL.CFM for the
form page
2.
See CH06_EX02-SOL.CFM
3.
See CH06_EX03-SOL.CFM
4.
See CH06_EX04-SOL.CFM
Project Building Exercises
Answers:
1. See ShoppingCart.cfm template
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