DISTINCT Clause
SELECT DISTINCT
removes all duplicate rows from the result set.
SELECT DISTINCT ON ( expression [, ...] )
keeps the first row of each set of rows that match the expression. The DISTINCT ON
expressions are interpreted using the same rules as ORDER BY. The first row of each set is random unless you use ORDER BY
.
Match the DISTINCT ON
expressions to the leftmost ORDER BY
expressions. The ORDER BY
clause normally contains additional expressions that determine the precedence of rows within each DISTINCT ON
group.
This example shows a select statement with DISTINCT ON
and ORDER BY
defined. The example retrieves the most recent weather report for each location. Without ORDER BY
the report returns a random time for each location.