CLAUSE: WHERE
DELETE [table | *] FROM table
WHERE selectcriteria
SELECT table | * FROM table
WHERE selectcriteria
UPDATE table SET newvalue
WHERE selectcriteria
The WHERE clause is used with the
DELETE, SELECT, and UPDATE statements
to specify a selection criteria.
However, the WHERE clause is optional.
Consider the following SELECT
example which does not use a WHERE.
This simple query will return
all rows from the table SongWriters:
SELECT * FROM SongWriters;
The addition of
a WHERE to the previous example allows you to efficiently narrow
the values that will be selected. In this example, we narrow the criteria
to only 'Jazz':
SELECT * FROM SongWriters WHERE MusicType='Jazz';
By using the AND logical operator we can further narrow the criteria:
SELECT * FROM SongWriters WHERE MusicType='Jazz' AND
YearWritten=1940;
You can also use the OR logical operator:
SELECT * FROM SongWriters WHERE MusicType='Jazz' OR
MusicType='Blues';
Within a WHERE clause, you can link up to a total of forty (40) expressions
using logicical operators:
SELECT * FROM SongWriters WHERE MusicType='Jazz' OR
MusicType='Blues' OR MusicType='Gospel' AND YearWritten>1939 AND YearWritten<1946;
Copyright 2000 by Infinite Software Solutions, Inc.
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