How can I delete duplicate rows in a table

Question

I have a table with say 3 columns. There\'s no primary key so there can be duplicate rows. I need to just keep one and delete the others. Any idea how to do this is Sql Serv

Answer 1

This is a way to do it with Common Table Expressions, CTE. It involves no loops, no new columns or anything and won't cause any unwanted triggers to fire (due to deletes+inserts).

Inspired by this article.

CREATE TABLE #temp (i INT)

INSERT INTO #temp VALUES (1)
INSERT INTO #temp VALUES (1)
INSERT INTO #temp VALUES (2)
INSERT INTO #temp VALUES (3)
INSERT INTO #temp VALUES (3)
INSERT INTO #temp VALUES (4)

SELECT * FROM #temp

;
WITH [#temp+rowid] AS
(SELECT ROW_NUMBER() OVER (ORDER BY i ASC) AS ROWID, * FROM #temp)
DELETE FROM [#temp+rowid] WHERE rowid IN 
(SELECT MIN(rowid) FROM [#temp+rowid] GROUP BY i HAVING COUNT(*) > 1)

SELECT * FROM #temp

DROP TABLE #temp