Removing Duplicate Rows in PostgreSQL with multiple columns

Here's an option

DELETE FROM votes T1    USING   votes T2WHERE   T1.ctid < T2.ctid     AND T1.voter = T2.voter     AND T1.election_year  = T2.election_year;

See http://sqlfiddle.com/#!15/4d45d/5

Delete from or updating CTEs doesn't work in Postgres, see the accepted answer of "PostgreSQL with-delete “relation does not exists”".

Since you have no primary key you may (ab)use the ctid pseudo column to identify the rows to delete.

WITHcteAS(SELECT ctid,       row_number() OVER (PARTITION BY voter,                                       election_year                          ORDER BY voter) rn       FROM votes)DELETE FROM votes       USING cte       WHERE cte.rn > 1             AND cte.ctid = votes.ctid;

db<>fiddle

And probably think about introducing a primary key.

The ctid field is a field that exists in every PostgreSQL table and is unique for each record in a table and denotes the location of the tuple.You did almost right just need ctid as you have no unique id for each row

;WITH CTE AS(SELECT ctid,voter,        election_year,       ROW_NUMBER()OVER(PARTITION BY voter, election_year ORDER BY voter) as RNFROM votes)delete  FROM votes v where v.ctid in (select CTE.ctid from  CTE where CTE.RN>1)

http://sqlfiddle.com/#!17/4d45d/14