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PostgreSQL : ORDER BY Clause

Tutorial by:      Date: 2016-04-19 04:17:21

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This PostgreSQL tutorial explains how to use the PostgreSQL ORDER BY clause with syntax and examples.

Description

The PostgreSQL ORDER BY clause is used to sort the records in your result set. The ORDER BY clause can only be used in SELECT statements.

Syntax

The syntax for the ORDER BY clause in PostgreSQL is:

SELECT expressions

FROM tables

[WHERE conditions]

ORDER BY expression [ASC | DESC | USING operator] [NULLS FIRST | NULLS LAST];

Parameters or Arguments

expressions

The columns or calculations that you wish to retrieve.

tables

The tables that you wish to retrieve records from. There must be at least one table listed in the FROM clause.

WHERE conditions

Optional. The conditions that must be met for the records to be selected.

ASC

Optional. It sorts the result set in ascending order by expression (default, if no modifier is provider).

DESC

Optional. It sorts the result set in descending order by expression.

NULLS FIRST

Optional. If specified, all NULL values sort before non-NULL values in the result set.

NULLS LAST

Optional. If specified, all NULL values sort after non-NULL values in the result set.

Note

  • If the ASC or DESC modifier is not provided in the ORDER BY clause, the results will be sorted by expression in ascending order. This is equivalent to ORDER BY expression ASC.

Example - Sorting without using ASC/DESC attribute

The PostgreSQL ORDER BY clause can be used without specifying the ASC or DESC modifier. When this attribute is omitted from the ORDER BY clause, the sort order is defaulted to ASC or ascending order.

For example:

SELECT last_name, first_name

FROM contacts

WHERE state = 'California'

ORDER BY last_name;

This PostgreSQL ORDER BY example would return all records sorted by the last_name field in ascending order and would be equivalent to the following ORDER BY clause:

SELECT last_name, first_name

FROM contacts

WHERE state = 'California'

ORDER BY last_name ASC;

Most programmers omit the ASC attribute if sorting in ascending order.

Example - Sorting in descending order

When sorting your result set in descending order, you use the DESC attribute in your ORDER BY clause as follows:

SELECT last_name, first_name, city

FROM contacts

WHERE first_name = 'Joe'

ORDER BY last_name DESC;

This PostgreSQL ORDER BY example would return all records sorted by the last_name field in descending order.

Example - Sorting by relative position

You can also use the PostgreSQL ORDER BY clause to sort by relative position (ordinal position) in the result set, where the first field in the result set is 1. The next field is 2, and so on.

For example:

SELECT last_name, first_name, city

FROM contacts

WHERE first_name = 'Jane'

ORDER BY 3 DESC;

This PostgreSQL ORDER BY would return all records sorted by the city field in descending order, since the city field is in position #3 in the result set and would be equivalent to the following ORDER BY clause:

SELECT last_name, first_name, city

FROM contacts

WHERE first_name = 'Jane'

ORDER BY last_name DESC;

Example - Using both ASC and DESC attributes

When sorting your result set using the PostgreSQL ORDER BY clause, you can use the ASC and DESC attributes in a single SELECT statement.

For example:

SELECT last_name, first_name, city

FROM contacts

WHERE first_name = 'Jane'

ORDER BY last_name ASC, first_name DESC;

This PostgreSQL ORDER BY would return all records sorted by the last_name field in ascending order, with a secondary sort by first_name in descending order.

 

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