CNF/DNF of OR is MVIndex, but mv index does not selected

[seiya-annie]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

SELECT item_primary_key FROM items WHERE
? member of (domains) OR
? member of (image_signatures) OR
? member of (canonical_links) OR
json_contains(feed_profile_ids, '[?]')
/+ this dnf item could be used as access condi since it has only one index path/
limit 10

2. What did you expect to see? (Required)

mv index can be selected

3. What did you see instead (Required)

9f9a201fe639fafc3984a2bac2cf792d8cb41e9e3989f92f4d14b244e827ce0e.txt

4. What is your TiDB version? (Required)

master

[AilinKid]

/** SQ8-2 **/
SELECT
  item_primary_key
FROM
  items
WHERE
  "B2c32" member of (domains)
  OR "2eoqyp6399" member of (image_signatures)
  OR "E33EAdAc2Bee.com/s/link" member of (canonical_links)
  OR json_contains(feed_profile_ids, '[69236881]')
LIMIT
  10;

since json_contains is INTERSECTION logic, the embedded INTERSECTION indexMerge inside UNION indexMerge is banned. Currently fallback to table scan is reasonable. Workaround you can manually split it into two subquery linked with UNION