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Unformatted text preview: criteria for complex queries, it can operate on
multiple tables at a time, and a specified criteria can be saved for future use.
Query By Example (QBE)
Although query languages are easy to learn and use, many database developers
further simplify the job of database users of specifying search criteria by providing
front ends for the query language that collect the facts about a query from the user
and compose query language statements internally. The front end usually consists
of a form (called QBE form) and the user simply specifies the search criteria by
inputting values into the fields of this form. Again the values may be input either
by typing them or by selecting an option from a set of options provided for a
particular field, depending on how the front end has been designed to work.
The QBE form is designed to collect all necessary information from the user for
composing query language statement(s) for the search criteria. Once the user
completes the QBE form, the QBE engine automatically converts the user inputs
into suitable query language statement(s) for search processing. Hence the user is
relieved of remembering the query language keywords and using them with the
correct syntax to form queries. This front-end feature is called query by example
(QBE) and has been found to be very userful for many database users, especially
The user of a database system can use the report generator of the database system
to assemble the output of a database query in the desired format. For this, the user
creates a report specifying the layout of the display (or printout) of the fields
requested by the user in the query. The user can also specify the titles and subtitles
for the report, the column headings for the various fields, and other elements to
make the output appear more presentable. Furthermore, the user can even specify
the output to be sorted with respect to one or more fields in the output. When the
sorting is on more than one field, the user has to specify the primary, secondary,
and tertiary key fields. A created report can be saved and used later for generating
similar reports whenever required. Figure 16.13 shows a sampl...
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This document was uploaded on 04/07/2014.
- Spring '14