Query
Commands
Query
A query is an operation, which will allow you to extract information
from a table (or tables) given particular criteria. For example,
you could search through a list for a stock item within a certain
price range, or a person in a certain town.
Query
Commands
When we search for information we don't always know the exact
details of the data we want to view. To help us we can use a structured
query language (SQL) which will allow us to select fields from
a database and then enter a range of values using arithmetic operators
like:
| > |
Greater
than |
| < |
Less
than |
| >= |
Greater
than or equal to |
| <= |
Less
than or equal to |
| = |
Equal
to |
| <> |
Not
equal to |
Other
words - eg. AND, OR and LIKE are also used to narrow a range.
Wildcard
commands are useful when you are not sure of the exact spelling
or how the information is stored. An asterisk, * placed at the
end or beginning of the search criteria represents any letter.
Suppose the police want to trace the owner of a white Audi with
a registration number where K is the last letter. A search for
Audi under Make of car, White under Colour and **K will pick out
a narrow range of vehicle owners from the database at the DVLA.
If
you are looking for a name in a database and you only know the
first 2 letters, for example Je, then Je* could bring up Jennings,
Jenkins, Jessop. If you know the exact name as it appears in the
database then you can type in the whole name.
 Contents:
Databases
Skill
Check: Databases
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