PostgreSQL SyntaxLesson 18Free preview

PostgreSQL SELECT DISTINCT

This lesson is part of PostgreSQL · All levels

Summary

SELECT DISTINCT displays only a unique value combination so that duplicate rows do not appear on the result. DISTINCT is applicable to all selected columns at once, not per column. PostgreSQL also provides DISTINCT ON to select one row per group according to the sequence rules.

Key points

DISTINCT eliminates duplicate rows from the query results.
Uniqueness is judged by a combination of all the selected columns.
DISTINCT ON (expression) selects one row per group by PostgreSQL.
COUNT(DISTINCT column) calculates the number of unique values.

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