Querying from Databases Flashcards
This process of accessing data is known as
Data retrieval
When choosing a system for data retrieval, the following factors are of importance
Performance
Capacity
Data Security
Cost
should be measured by the time it takes for data to be retrieved and the number of requests that can be processed at one time.
Performance
refers to not just the number of files that can be stored, but also how large each file can be.
Capacity
Protecting the information from people who are not authorized to view it is a function of data security.
Data Security
There are three areas of concern involving cost
support personnel
software
and hardware
developed by the mathematician George Boolein the 1800s, is used to search databases and is recognized by most search engines, such as Google. Search is conducted for keywords connected by the operators AND, OR, and NOT.
Boolean Logic
Boolean searching is often used with
Truncations and wildcards
The most common use of structured query language(SQL) is
to obtain and display information from databases.
Used with a number of optional keywords and extensions to access table data.
SELECT
shortcut to indicate all columns, such as SELECT*FROM customers
Asterisk (*)
used to list and separate specific columns, such as SELECT PatientID, LastName, FirstName, FROM County
Comma (,)
limits the number of rows, such as SELECT PatientID, LastName, FirstNAME, From County = ‘Monterey’
WHERE
eliminates, such as FROM County <> ‘Monterey’
NOT or <>
limits, such as WHERE Service Date BETWEEN “1-july-2011’ AND ‘1-September-2011’
BETWEEN
