Computer Programming Concepts and Visual Basic David I. Schneider

350 Computer Programming Concepts and Visual Basic
SUMMARY
1. A table is a group of data items arranged in a rectangular array, each containing
the same categories of information. Each data item (row) is called a record.
Each category (column) is called a field. Two tables with a common field are
said to be related. A database is a collection of one or more, usually related,
tables.
2. The data control is used to access a database. When a text box is bound to a
data control through its DataSource and DataField properties, the user can read
and edit a field of the database. At any time, one record is specified as the
current record. The user can change the current record with the data control’s
navigator arrows or with Move statements. The property RecordCount count
records, the property BOF indicates whether the beginning of the recordset has
been reached, and the property EOF indicates whether the end of the recordset
has been reached. The Value property of Fields (“fieldName”) reads the contents
of a field of the current record. The Validate event, which can be used to
control edits, is triggered whenever the current record is about to be changed.
3. A primary key is a field or set of fields that uniquely identifies each row of a
table. The rule of entity integrity states that no record can have a null entry in a
primary key. A foreign key is a field or set of fields in one table that refers to a
primary key in another table. The rule of referential integrity states that each
value in the foreign key must also appear in the primary key.
4. Structured Query Language (SQL) is used to create a “virtual” table consisting
of a subtable of a table or of a join of two tables and imposes an order on the
records. The subtable is specified with the reserved words SELECT, FROM,
WHERE, ORDER BY, and INNER JOIN . . . ON. The WHERE clause of an
SQL statement commonly uses the Like operator in addition to the standard
operators. SQL statements are either employed at design time or run time as the
setting of the RecordSource property. During run time, the Refresh method for
the data control should be executed after the RecordSource property is set.
5. The MS FlexGrid grid control can show an entire “virtual” table in a spreadsheet-like
display. Data-bound list box and data-bound combo box controls can
display the contents of a single field for an entire table or recordset.
6. Visual Data Manager, a database management program supplied with most versions
of Visual Basic, can be used to create a database and specify primary keys
and validation criteria. A database can be created by code with the Professional
or Enterprise editions of Visual Basic.
7. Although good database design is an art, there are several fundamental principles
that usually should be followed.
PROGRAMMING PROJECTS
1. The database MICROLND.MDB (on the accompanying CD) is maintained by
the Microland Computer Warehouse, a mail order computer supply company.
Tables 11.7 through 11.9 show parts of three tables in the database. The table
Customers identifies each customer by an ID number and gives, in addition to
the name and address, the total amount of purchases during the current year.
The table Inventory identifies each product in stock by an ID number and gives,
in addition to its description and price (per unit), the quantity currently in stock.
The table Orders gives the orders received today. Suppose it is now the end of
the day. Write a program that uses the three tables to do the following: