DISTINCT ON

Learn DISTINCT ON in PostgreSQL through the exact construct, a dedicated example, a boundary case, and a mastery check.

10 min read • Beginner

DISTINCT ON is an atomic PostgreSQL lesson inside Core PostgreSQL. The example uses the specific syntax, command, API, instruction, or language rule named by this lesson.

Study the construct itself, then change one relevant input and predict the result before running it. That keeps this lesson focused on DISTINCT ON rather than on generic PostgreSQL syntax.

Topic-specific example

postgresql-01-04.sql

sql Try It Live

SELECT DISTINCT ON (customer_id) customer_id,id,created_at FROM orders ORDER BY customer_id,created_at DESC;

Edge case / engineering note

Test DISTINCT ON with an empty result, NULL/missing value, duplicate key, or concurrent operation where relevant; database behavior should be verified at the boundary shown by this example.

Content source & attribution

Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

DISTINCT ON Mastery Check →

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DISTINCT ON

Topic-specific example

Lesson quizzes

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