NonStop Systems Introduction

The Relational Database Management System
NonStop Systems Introduction—527825-001
4-3
Logical Views of Data
Logical Views of Data
With SQL/MX, logical views of data in the tables are obtained through data definition
statements rather than from application code. Data definitions can limit a view to
selected columns of data or expand it to a new combination of data from two or more
tables. Figure 4-2 on page 4-4 shows a view that was created by extracting two
columns from the EMPLOYEE table and one column from the DEPARTMENT table.
One of the jobs of a database administrator is to create views like the one shown in
Figure 4-2 and store the view definition so that programmers and end users can use
the view as needed.
The use of views cuts down on coding steps for programmers. Programmers do not
need to specify special selection criteria every time they include a particular query in
an application program.
Figure 4-1. A SQL/MX Relational Database
100
250
• • •
MANAGER
ASSEMBLER
JOB TABLE
900
JOBCODE JOBDESC
• • •
DEPARTMENT TABLE
1000
1500
FINANCE
PERSONNEL
23
213
9000
1000
CHICAGO
CHICAGO
CHICAGO
• • • • • • • • • • • • • • •
DEPTNUM DEPTNAME MGR RPTDEPT LOCATION
VST044.vsd
EMPLOYEE TABLE
EMPNUM FNAME LNAME
DEPTNUM JOBCODE SALARY
1
23
ROGER
JERRY
GREEN
HOWARD
4000
1000
100
200
75500.00
37000.00
• • • • • • • • • • • • • • •• • •
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