SQL Update statement with 2 EXISTS clause - mysql

Question

I am trying to update a value to be NULL where tracker_unique_id can be found in ab_split_tracker_unique_link where that ones ab_split_id can be found in a 3rd table ab_split_candidate.
I cant do it by giving it different values as they can be different from user to user on locals
UPDATE trustpilot_links SET `invite_after_enquiry` = NULL
WHERE EXISTS (
SELECT tracker_unique_id, ab_split_tracker_unique_link.ab_split_candidate_id
FROM ab_split_tracker_unique_link
WHERE EXISTS (
SELECT ab_split_candidate_id
FROM ab_split_candidate LEFT JOIN ab_split
ON ab_split_candidate.ab_split_id = ab_split.ab_split_id WHERE ab_split.reference="review_invite_after_enquiry"
)
);
Edit:
Table examples
Trustpilot Links
trustpilot_link_id | invite_after_enquiry | tracker_unique_id
1 1 123
2 0 1234
ab_split_tracker_unique_link
tracker_unique_id | ab_split_id
1234 32
Ab Split
ab_split_id | reference
32 review_invite_after_enquiry
I want to set values to null if there tracker cannot be found in table ab_split_tracker_unique_link with an ab_split_id that is equal to review_invite_after_enquiry in ab_split

Answer 1

Your subqueries are not related to their parent queries as they should be. Let's look at your inner-most query:
SELECT ab_split_candidate_id
FROM ab_split_candidate
LEFT JOIN ab_split ON ab_split_candidate.ab_split_id = ab_split.ab_split_id
WHERE ab_split.reference = 'review_invite_after_enquiry'
Well, first of all your WHERE clause dismisses outer-joined records, so this is essentially an INNER JOIN. But then: either there are such records or not. This has nothing to do with the record your are potentially updating, nor with the ab_split_tracker_unique_link you are looking up.
So either you are updating all records or none.
We would rather expect something like
UPDATE trustpilot_links tl
SET invite_after_enquiry = NULL
WHERE EXISTS
(
SELECT *
FROM ab_split_tracker_unique_link stul
WHERE stul.tracker_unique_id = tl.tracker_unique_id
AND ...
);
So add WHERE clauses that relate the subqueries to their parent queries.