NonStop Systems Introduction for H-Series RVUs

The Relational Database Management System
NonStop Systems Introduction for H-Series RVUs—540083-001
4-2
Easy Navigation Between Relational Tables
develop and use, but they were not powerful enough for a high-volume production
environment.
The basic contribution of SQL/MX to the real-time 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.
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.
Notice 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.