Delete from t from tovary t, tovary v

where t.tovar = v.tovar

and t.id > v.id

Сообщение 208, уровень 16, состояние 1, строка 1
Недопустимое имя объекта "tovar".

Select Tovar, Count(*) from Tovary Group by Tovar having Count(*) > 1

Delete t from tovary t, tovary v

Delete [Похожий] from tovary [Похожий], tovary [Исходный]

where [Похожий].tovar = [Исходный].tovar

and [Похожий].id > [Исходный].id

WITH CTE(N) AS(SELECT ROW_NUMBER()OVER(PARTITION BY tovar ORDER BY id) FROM tovary)
DELETE CTE WHERE N>1;