Introduction to Data Management

Accessing Databases With NonStop SQL
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The dictionary is actually composed of individual data catalogs—it is the set of all
SQL catalogs in the network. Each catalog is a group of predefined tables—one table
for each type of object in the database. Some of these tables provide most of the
information you need about your database, while others contain information used
only by NonStop SQL. For a database that resides on a single system, you can create a
single catalog for the entire database or use multiple catalogs to describe selected
portions of the database. For a distributed database, there is a separate catalog on
each system where a portion of the database resides. Because a catalog is itself a
relational database, you can query catalog tables just as you would query any tables in
your business database.
When an application frequently accesses a table by a particular column or set of
columns, you can speed query execution by creating an index based on those
columns. An index is simply an alternate access path that differs from the access path
(or primary key) defined when the table was created. The index information is stored
in the data dictionary and in other locations. An index improves access speed. An
index is useful for looking up table values in a sequence different from primary key
sequence or using a value different from a primary key value. Effectively, an index
provides an alternate key sequence for your table. Indexes can be added as needed
and deleted when no longer needed, both without affecting the indexed table in any
way.
Database administration is handled primarily through SQLCI, as shown in Figure 3-8.
You enter interactive data definition language statements to create, alter, and delete
the objects registered in a catalog. You enter data manipulation statements to query
and report on the data dictionary. You enter utility statements to specify data
security, load and copy data, monitor application performance, manage a distributed
database, and manipulate database files.