The syntax of the optional
BY clause is as follows:
ORDER BY expression [ ASC | DESC ] [, ...]
expression can be the name or ordinal number of an output column in the
SELECT list. It can also be an arbitrary expression formed from input-column values.
ORDER BY clause causes the result rows to be sorted according to the specified expressions.
If two rows are equal according to the leftmost expression, they are compared according
to the next expression. If they are equal according to all specified expressions,
they are returned in an implementation-dependent order.
The ordinal number refers to the ordinal (left-to-right) position of the result column.
This feature enables sorting based on a column that does not have a unique name. This
is not necessary because you can use the
AS clause to assign a name to a result column.
You can also use arbitrary expressions in the
BY clause, including columns that do not appear in the
SELECT output list. Therefore, the following statement is valid:
SELECT ename FROM emp ORDER BY empno;
ORDER BY clause applying to the result of a
MINUS clause can specify only an output column name or number rather than an expression.
ORDER BY expression is a simple name that matches both an output column name and an input
ORDER BY interprets it as the output column name. This is the opposite of the choice made
GROUP BY clause in the same situation. This inconsistency is made to be compatible with the
You can add the ASC (ascending) or DESC (descending) keyword after any expression
ORDER BY clause. If you specify neither ASC nor DESC, ASC is used.
The null value is sorted in a higher order than other values. In other words, null values are at the end of an ascending order and are at the beginning of a descending order.
String data is sorted based on the sorting rule set for specific regions created when the database cluster is initialized.
The following two examples show how to sort the results based on the content of the second column (dname):
SELECT * FROM dept ORDER BY dname; deptno | dname | loc --------+------------+---------- 10 | ACCOUNTING | NEW YORK 40 | OPERATIONS | BOSTON 20 | RESEARCH | DALLAS 30 | SALES | CHICAGO (4 rows) SELECT * FROM dept ORDER BY 2; deptno | dname | loc --------+------------+---------- 10 | ACCOUNTING | NEW YORK 40 | OPERATIONS | BOSTON 20 | RESEARCH | DALLAS 30 | SALES | CHICAGO (4 rows)