Unformatted text preview: or all fields.
The Find command cannot be used for creating an elaborate set "of criteria for
complex queries. Furthermore, it can operate on only one table at a time, and the
user cannot save a specified criteria for future use.
For handling complex quieries, all database systems support a query language.
Most of these query languages conform to the SQL standard. In SQL, the user has
to specify the criteria for search along with the fields and table (or tables) with
which to work with. The criteria for search can be built by using the relational
operators (= [equal to], > [greater than], < [less that], and combinations of these
operators) and the logical operators (AND, OR, and NOT). For example, to list out
the names of all employees whose last name starts with the letter "S", who belong
to "PUNE", and whose age is more than 40 years, the SQL query will look as
SELECT [LAST NAME], [FIRST NAME], [MIDDLE NAME]
WHERE ([LAST NAME] = "S..") AND (CITY = "PUNE") AND [AGE > 40])
The keywords SELECT, FROM, and WHERE tell the SQL engine how to
interpret each part of the query statement. The SELECT keyword tells SQL which
fields are to be displayed for the records that match the criteria. The FROM
keyword tells SQL which table(s) to work with. The WHERE keyword tells SQL
the criteri for selecting the records (search criteria). The brackets [...] around some
of the field names are needed in the above example because these field names
contain spaces, and the brackets help the database to interpret each field name
correctly. A query language can be easily learnt and used even by a non-programmer
because the complexity of a query language statement is normally more or less of
the same order as given in the above SQL statement. Furthermore, a query
language uses only a few keywords which are easy to remember and use. In fact,
SQL has only a few dozen or so basic keywords.
Other advantages of using a query language are that a query statement can be used
for creating an elaborate set of...
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- Spring '14