How to delete from select in MySQL?

Question

SELECT (sub)queries return result sets. So you need to use IN, not = in your WHERE clause.

Additionally, as shown in this answer you cannot modify the same table from a subquery within the same query. However, you can either SELECT then DELETE in separate queries, or nest another subquery and alias the inner subquery result (looks rather hacky, though):

DELETE FROM posts WHERE id IN (
    SELECT * FROM (
        SELECT id FROM posts GROUP BY id HAVING ( COUNT(id) > 1 )
    ) AS p
)

Or use joins as suggested by Mchl.

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