All Clauses
DELETE Statement
SELECT Statement
UPDATE Statement
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
;
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