NonStop Systems Introduction

The Relational Database Management System
NonStop Systems Introduction—527825-001
4-2
Easy Navigation Between Relational Tables
applications. These applications were easy to develop and use, but they were not
powerful enough for a high-volume production environment.
To achieve high performance, programmers developed transaction processing
applications based on nonrelational database management systems. These
applications were capable of processing a large volume of transactions, but they were
very hard to develop and maintain because of the complexities of the underlying
DBMS. In contrast to nonrelational systems and other SQL implementations, SQL/MX
offers both high performance and high productivity in the same DBMS.
The basic contribution of SQL/MX to the ZLE application environment is high
performance and ease of use. The following discussion focuses on the other features
of this powerful product.
Easy Navigation Between Relational Tables
SQL/MX uses the relational database model: two-dimensional tables consisting of rows
and columns. A relational table is a logical representation of an underlying physical
file. Each row represents a record in the physical file, and each column represents a
field common to all the records in the physical file.
For easy data access, the relational approach navigates between tables by using
columns of common data instead of links and pointers to physical locations. Figure 4-1
on page 4-3 shows an SQL/MX database consisting of three tables:
•
The EMPLOYEE table contains one row for each employee. Each row contains
columns that hold facts about an employee, such as employee number, first name,
and last name.
•
The DEPARTMENT table contains one row for each department. The columns in
each row hold facts about the department, such as department number and name.
•
The JOB table contains one row for each type of job. The columns of each row
give the job code and job description for a particular job.
Note that there is a common JOBCODE column in the EMPLOYEE and JOB tables,
and a common DEPTNUM column in the EMPLOYEE and DEPARTMENT tables. An
SQL SELECT statement in an application program could easily obtain information from
all three tables simply by supplying the employee number (EMPNUM) and asking
SQL/MX to find the salary (SALARY column), department name (DEPTNAME column),
and job description (JOBDESC column) for the employee.