Oracle® Database SQL Reference 10g Release 2 (10.2) Part Number B14200-02 |
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Use the ORDER
BY
clause to order the rows selected by a query. Sorting by position is useful in the following cases:
To order by a lengthy select list expression, you can specify its position in the ORDER
BY
clause rather than duplicate the entire expression.
For compound queries containing set operators UNION
, INTERSECT
, MINUS
, or UNION
ALL
, the ORDER
BY
clause must specify positions or aliases rather than explicit expressions. Also, the ORDER
BY
clause can appear only in the last component query. The ORDER
BY
clause orders all rows returned by the entire compound query.
The mechanism by which Oracle Database sorts values for the ORDER
BY
clause is specified either explicitly by the NLS_SORT
initialization parameter or implicitly by the NLS_LANGUAGE
initialization parameter. You can change the sort mechanism dynamically from one linguistic sort sequence to another using the ALTER
SESSION
statement. You can also specify a specific sort sequence for a single query by using the NLSSORT
function with the NLS_SORT
parameter in the ORDER
BY
clause.
See Also:
NLSSORT and Oracle Database Globalization Support Guide for information on the NLS parameters