Computer Programming Concepts and Visual Basic David I. Schneider

TABLE 11.5(B)
TABLE 11.5(C)
course section time
CS102 1001 MWF 8–9
CS102 1002 MWF 1–2
CS102 1003 MWF 2–3
CS102 1004 MWF 3–4
CS105 1001 MWF 1–2
course name credits prerequisite
CS102 Intro to Databases 3 CS101
CS105 Visual Basic 4 CS200
Avoid tables with intentionally blank entries.
Tables with entries that are intentionally left blank waste space and are inefficient to use.
Table 11.6, which serves as a directory of faculty and students, has an excessive number of
blank entries. The table should be split into two tables, each dealing with just one of the
groups.
TABLE 11.6
A Table with an Excessive Number of Blank Entries
name ssn classifi- date office credits
cation hired dept number gpa earned
Sarah Brown 816-34-9012 student 3.7 78
Pat Riley 409-22-1234 faculty 9/1/90 biology Y-3014
Joe Russo 690-32-1108 faculty 9/1/88 math T-2008
Juan Lopez 509-43-4110 student 3.2 42
Strive for table clarity.
Each table should have a basic topic and all the data in the table should be connected to that
topic.
Don’t let a table get unnecessarily large.
A bookstore might keep a permanent record of each purchase for the purpose of targeting
mailings. A better solution is to add a couple of extra fields to the customer table that identify
the types of books of interest to the customer.
Avoid fields whose values can be calculated from existing fields.
A calculated field is one whose value can be determined from other fields. For instance, if a
table has fields for both the population and area of a state, then there is no need to include a
field for the population density.
COMMENTS
Creating and Designing Databases 349
1. Visual Data Manager can not create foreign keys.
2. You can add additional fields to a database table, but you cannot rename, modify,
or delete fields without deleting the entire table and rebuilding each field.
For this reason, design your tables carefully.
3. The total length of a record in a table is limited to 2000 bytes.
4. Be careful if you create a database with empty tables. If you pull it into a program
and try to move through it with the navigator arrows, an error will be generated.
You must add at least one record before starting to navigate.