CHAPTER 1: Introduction

A database management system is an integrated system of computer programs and files for organizing, storing, and retrieving data.

A relational database management system (RDBMS) organizes data into structures known as relations or tables. Each table is identified by a unique table name, and has a fixed number of columns and a variable number of rows. The columns are called attributes and each is labeled with an attribute name. All data values under a given attribute are of the same type, such as integer or character. Each row in a table is called a record, or tuple, with one data value for each attribute.

Tables may be created or removed from the database as required. New records may be added to them, and existing records may be updated or deleted. Most importantly, data may be selectively retrieved from tables according to certain criteria. These criteria usually involve the values of one or more of the attributes of given tables. For example, you may retrieve all the records from a table where one attribute has some specific value.

Most commands to a database management system are issued via a Structured Query Language (SQL), which is similar in form to a natural language. Structured Query Language commands are often referred to simply as "queries".

Empress is a relational database management system. With Empress you can use English-like commands to create a new database, query a database for information, and manage the information in a database. Commands may be used conversationally from a terminal, submitted in batches from files, or embedded in an application program.

Empress has an SQL language which uses simplified English sentences, making it easy to learn and straightforward to use. Generally, commands to do something, such as insert data into a table or select data from one, are phrased in the SQL language much as they would be in English.

This manual contains syntax reference for the Empress Query Language commands. Other topics, such as command logging, the database loader, export/import utilities, the data dictionary, administrative variables, system supplied help and adding customized help files are discussed in the Empress: Database Administrator's Guide.

Note that this manual is not a tutorial, the examples in this manual section are based on the tables personnel, loans, auto parts, and customers described in this chapter. The effects of previous commands are not considered when the output of a command is shown.

Examples given in this manual feature a database called repairs which contains these four tables:

1. A personnel table of personnel records which containing employees' personnel numbers, names, phone numbers, and credit limits for loans. It has attributes named number, name, phone, and credit_limit. The personnel table has one record for each employee.

2. A loans table containing information about loans made to employees which contains the employee's name, the date on which the loan was made, and the amount. It has attributes called number, name, date, and amount. The loans table may have more than one record for each employee.

3. An auto parts table which holds records of various auto part suppliers with the attributes supplier, phone, part name, part no., and price.

4. A customers table which holds customers' names and addresses, and some comments about them with the attributes name, address, and comments.

The four tables hold the following data:

*** Table: personnel ***

number	name	phone	credit_limit
10	Kilroy	426-9681	$500.00
5	Mosca	544-2243	$750.00
17	Wladislaw	723-6073	$50.00
3	Jones	667-2951	$500.00
8	Peterson	978-6060	$250.00
4	Scarlatti	961-7363	$100.00
9	Jordan	964-3335	$250.00

*** Table: loans ***

number	name	date	amount
5	Mosca	2 February 1990	$150.0
3	Jones	7 February 1990	$33.95
10	Kilroy	16 February 1990	$250.00
17	Wladislaw	27 February 1990	$55.00
3	Jones	3 April 1990	$25.00
5	Mosca	4 May 1990	$200.00
17	Wladislaw	12 May 1990	$25.00
8	Peterson	6 June 1990	$50.00
17	Wladislaw	25 June 1990	$75.00
3	Jones	12 August 1990	$300.00
4	Scarlatti	9 September 1990	$150.00
4	Scarlatti	14 October 1990	$125.00

*** Table: auto parts ***

supplier	phone	part name	part no.	price
AAA Automotive	922-8624	Hubcap	9836653	$18.40
AAA Automotive	922-8624	Fender rubber	9837521	$47.95
AAA Automotive	922-8624	Fender chrome	9837522	$67.95
Rick's Repairs	675-4436	Spark plugs	243	$1.25
Speedy Body Shop	643-8994	Rear wing	87003	$75.00
Speedy Body Shop	643-8994	Front wing	87005	$79.99
Rick's Repairs	675-4436	Radiator	493	$175.00
Auto Wholesalers	922-6219	Spray paint	2198	$1.25
Auto Wholesalers	922-6219	Chrome paint	3286	$1.99

*** Table: customers ***

name	address	comments
Mr. R. Lucas	1423 Beach Drive, Bayville, CA 92308	Can always be sold something new and flashy - like chrome and colored stuff, also little gadgets.
Mr. J. Phillips	63 Shore Bvde., Gull Point, CA 92309	Pays bills 2 months late -- needs to be threatened with a collection agency.
Mr. B. Wilson	14 Valley View Drive, Bayville, CA 92308	Good customer -- give credit if he asks for it.
Ms. C. Marshall	12 Berkeley St., Gull Point, CA 92309	Suggest vacuum & wash; she keeps 3 dogs. Look for dog hair collecting in engine.
Mr. J. Lee	3260 Church St., Gull Point, CA 92309	Father pays bills -- check with R. Lee before accepting a job, but don't let Johnny know you're doing so.

In the following chapters, the personnel, loans, auto parts, and customers tables will be used extensively to illustrate the various Empress features and commands.

The commands and syntax used to create the tables are found in the CREATE TABLE command in this manual.