Database Basics

Date: 2015-10-07; view: 557.

Today you begin to learn about database programming in Delphi. If you are new to database programming, at first glance it might appear overwhelming. Today I'll try to eliminate any confusion by presenting a clear picture of the labyrinth known as database programming. First, I'll give you an overview of the Delphi database architecture. After that I'll go over some of the data access components.

Make no mistake: Database programming is complicated. I'll give you a high-level view of database programming in Delphi, but I won't attempt to cover every detail.

NOTE: Not all the concepts and components discussed in this chapter pertain to every version of Delphi. The Professional version of Delphi has more database capabilities than the Standard version. The Client/Server version of Delphi has many more database capabilities than either the Standard or Professional version.

Database programming comes with a whole gaggle of buzzwords: BDE, client, server, ODBC, alias, SQL, query, stored procedure, and so on. The good news is that it isn't all that bad after you learn some basics. First, let's take a moment to talk about databases. When you hear the word database, you probably imagine data stored in table format. The table probably contains fields such as FirstName, LastName, and PhoneNumber. These fields are filled with data to create individual records in a database file.

If that's what you envision when you think of a database, you're not too far off, but you aren't exactly correct, either. The term database is used to describe an all-encompassing data creation and maintenance system. It is true that a database can be as simple as one table. On the other hand, a real-world database can include dozens or even hundreds of tables with thousands or millions of records. These tables can contain one or more indexes. A complete client/server SQL database solution can also contain numerous queries and stored procedures. (Don't worry; I'll explain some of these terms later in the chapter.) So as you can see, a database is more than just a table with data.

Speaking of tables, let's quickly cover some table basics. A table consists of at least two parts: fields and records. Fields are the individual categories of data in a table. For example, a table containing a n address book would have a field called FirstName, a field called LastName, one called Address, PhoneNumber, and so on. Fields are also referred to as columns. A record, then, is one person's complete address: first name, last name, address, and so on. Records are also called rows.

A database is just a collection of data, of course, but database tables are often displayed in spreadsheet format. The column headers across the top indicate the field names. Each row in the table contains a complete record. FIGURE 1.1 shows just such a database table displayed in grid (or table) format.

FIGURE 1.1.A typical database table.

New Term: The pointer to the current record within a database is called the cursor.

The cursor points to the record that will be read if data is requested and the record that will be updated if any edits are made. The cursor is moved when a user browses the database, inserts records, deletes records, and so on.

NOTE: When I say the cursor is a pointer, I don't mean it's a pointer in the Object Pascal sense. I merely mean it is an indicator of the current record's position.

New Term: A collection of data returned by a database is called a dataset.

A dataset can be more than just the data contained in a table. A dataset can be the results of a query containing data acquired from many tables. For example, let's say you have a database containing names and addresses of your customers, their orders, and the details of each order. This data might be contained in tables named Clients, Orders, and Order Details. Now let's say you request the details of the last 10 orders placed by Company X. You might receive a dataset containing information from the Clients table, the Orders table, and the Order Details table. Although the data comes from several different sources, it is presented to you as a single dataset.