Deleting duplicates

Administrative Snippets

Deleting duplicates

Works with PostgreSQL

8.4+

Written in

SQL

Depends on

Nothing

A frequent question in IRC is how to delete rows that are duplicates over a set of columns, keeping only the one with the lowest ID.

This query does that for all rows of tablename having the same column1, column2, and column3.

DELETE FROM tablename
WHERE id IN (
    SELECT
        id
    FROM (
        SELECT
            id,
            row_number() OVER w as rnum
        FROM tablename
        WINDOW w AS (
            PARTITION BY column1, column2, column3
            ORDER BY id
        )

    ) t
WHERE t.rnum > 1);

Sometimes a timestamptz field is used instead of an ID field.