使用子选择删除

Question

I am looking to delete via a subselect. The answers for this question do not solve my issue: MySQL Error 1093 - Can't specify target table for update in FROM clause .

I found a hackish way to do this and wanted to get feedback on if this was the most optimal solution for doing a DELETE with SUBSELECT --

DELETE FROM main_history WHERE id NOT IN (
   SELECT * from (
     SELECT max(id) FROM main_history h GROUP BY instance_id, xpath
   ) x
)

Basically, I just add in a second (meaningless) subselect to get around the mysql error, which I receive if I just do a normal DELETE with the subselect:

DELETE FROM main_history WHERE id NOT IN (
  SELECT max(id) FROM main_history h GROUP BY instance_id, xpath
);

You can't specify target table 'main_history' for update in FROM clause

Is this a good solution to the above issue?

Update: The subselect query performs much better than the join query. Here were my findings:

# 12m Subselect
DELETE FROM main_history WHERE id NOT IN (
 SELECT * from (
  SELECT max(id) FROM main_history h GROUP BY instance_id, xpath
 ) x
)

---

# 18m Join
Delete m1 from main_history m1 left join
(
  SELECT max(id) id FROM main_history h GROUP BY instance_id, xpath
) m2 on m1.id = m2.id
Where m2.id is null;

Answer 1

Right way is using delete join:

Delete m1 from main_history m1 left join
(
  SELECT max(id) id FROM main_history h GROUP BY instance_id, xpath
) m2 on m1.id = m2.id
Where m2.id is null;

Answer 2

You can use a derived table like this, then MySQL cant see the tablename from the SELECT:

DELETE FROM main_history WHERE id NOT IN (
   SELECT * FROM (
      SELECT * from (SELECT max(id) FROM main_history h
      GROUP BY instance_id, xpath) AS x
   ) AS delrows
);