Jul/090
What is a Database
Definitions:
A database is a collection of information organized into interrelated tables of data and specifications of data objects.
A table in a relational database is a predefined format of rows and columns that define an entity.
Database tables are composed of individual columns corresponding to the attributes of the object.
In a relational database, a row consists of one set of attributes (or one tuple) corresponding to one instance of the entity that a table schema describes.
Also Known As: Record
A single data item related to a database object. The database schema associates one or more attributes with each database entity.
Also Known As: field, column
A database record consists of one set of tuples for a given relational table. In a relational database, records correspond to rows in each table.
Databases are designed to offer an organized mechanism for storing, managing and retrieving information. They do so through the use of tables. If you’re familiar with spreadsheets like Microsoft Excel, you’re probably already accustomed to storing data in tabular form. It’s not much of a stretch to make the leap from spreadsheets to databases. Let’s take a look.
Database Tables
Just like Excel tables, database tables consist of columns and rows. Each column contains a different type of attribute and each row corresponds to a single record. For example, imagine that we were building a database table that contained names and telephone numbers. We’d probably set up columns named “FirstName”, “LastName” and “TelephoneNumber.” Then we’d simply start adding rows underneath those columns that contained the data we’re planning to store.
If we were building a table of contact information for our business that has 50 employees, we’d wind up with a table that contains 50 rows.
Databases and Spreadsheets
At this point, you’re probably asking yourself an obvious question – if a database is so much like a spreadsheet, why can’t I just use a spreadsheet? Databases are actually much more powerful than spreadsheets in the way you’re able to manipulate data. Here are just a few of the actions that you can perform on a database that would be difficult if not impossible to perform on a spreadsheet:
* Retrieve all records that match certain criteria
* Update records in bulk
* Cross-reference records in different tables
* Perform complex aggregate calculations
Jul/090
What is Oracle PLSQL
PL/SQL is Oracle’s SQL++ programming language providing structure and flow control extensions to SQL. The name PLSQL is derived from the term “Procedural Language extensions to SQL”.
On its own, SQL enables you to specify what you want done but not how it is done. However, you often need more control over how data is retrieved and manipulated and this is where PL/SQL comes in.
The procedural capabilities combined with standard SQL in Oracle PLSQL gives developers far more control of how their SQL statements interact with the database and makes using PL/SQL an excellent alternative to developing applications in other languages such as Java or C or VB.
The language itself is modeled on Ada, so Java/C/C++ programmers will find the syntax rather strange and probably won’t like the single”=” being used for comparison, but anyone who’s used Pascal or Ada or Modula2 will fell right at home.
PL/SQL is not a pure object-oriented language like Java or Ada, but it does support some obect-oriented features such as classification, polymorphism and, in the later versions, inheritance.