Error 1093 when trying to perform delete in MySQL - mysql

Question

A little help with this query please. When trying to perform a delete in MySQL, it returns an error: "MySQL Error 1093 - Can't specify target table for update in FROM clause". The select statement works fine otherwise. Here's the script:
DELETE
FROM redcap_data
WHERE record IN (SELECT DISTINCT
redcap_data.record,
redcap_data.field_name,
redcap_data.value
FROM redcap_metadata
INNER JOIN redcap_data
ON redcap_metadata.project_id = redcap_data.project_id
INNER JOIN redcap_events_metadata
ON redcap_data.event_id = redcap_events_metadata.event_id
INNER JOIN redcap_events_arms
ON redcap_events_metadata.arm_id = redcap_events_arms.arm_id
WHERE (redcap_data.project_id = '50'
AND redcap_events_arms.arm_num = '6'
AND redcap_data.record IN ('record_ids go here')
))

Answer 1

Try using an inner join on the subselect you are using as IN clause instead of the IN clause
DELETE r.*
FROM redcap_data r
INNER JOIN (
SELECT DISTINCT
redcap_data.record,
redcap_data.field_name,
redcap_data.value
FROM redcap_metadata
INNER JOIN redcap_data
ON redcap_metadata.project_id = redcap_data.project_id
INNER JOIN redcap_events_metadata
ON redcap_data.event_id = redcap_events_metadata.event_id
INNER JOIN redcap_events_arms
ON redcap_events_metadata.arm_id = redcap_events_arms.arm_id
WHERE (redcap_data.project_id = '50'
AND redcap_events_arms.arm_num = '6'
AND redcap_data.record IN ('record_ids go here')
)) t ON r.record = t.record

Answer 2

It's a documented restriction in MySQL.
One workaround is to use an inline view (derived table), and reference that in a JOIN operation.
Write it as SELECT first
SELECT t.*
FROM target_table t
JOIN ( SELECT q.id
FROM target_table q
JOIN ... r
ON ...
WHERE ...
GROUP BY ...
HAVING ...
) s
ON s.id = t.id
Then we can convert that to a DELETE statement. In my experience, the inline view gives enough separation of target_table in the outer query, that it doesn't raise the MySQL error.
At the time the outer query runs, the query that materializes derived table s has already been executed. The operations that MySQL performs is akin to this (not exactly this, but this illustrates the pattern, how we can think about the derived table ...
CREATE TEMPORARY TABLE _s_ ... ;
INSERT INTO _s_ (...) SELECT ... FROM target_table q ... ;
DELETE t.*
FROM target_table t
JOIN _s_
ON ...
;
DROP TEMPORARY TABLE _s_ ... ;
At the time the DELETE statement runs, it doesn't matter that target_table is referenced in the preceding SELECT. The work to materialize the temporary table s has already been done.