Difference in queries

gistfile1.txt

Runs in <1s:

SELECT UserEntity.*
FROM  (
	SELECT UserCoverageEntity.user_id
	FROM UserCoverageEntity 
	WHERE UserCoverageEntity.id=UNHEX('11e9e4e9c970a3f4857698fa9b0d2efc')
	UNION
	SELECT UserSchemeEntity.user_id
	FROM UserSchemeEntity
	LEFT JOIN SchemeCategoryEntity ON SchemeCategoryEntity.id=UserSchemeEntity.schemeCategory_id
	WHERE SchemeCategoryEntity.scheme_id=UNHEX('11e9ded018e2ac0eac7098fa9b0d2efc')
) AS b
LEFT JOIN UserEntity ON  b.user_id=UserEntity.id

B: Full table scan > 10s:
SELECT UserEntity.*
FROM UserEntity
WHERE UserEntity.id IN (SELECT UserEntity.id FROM UserEntity
INNER JOIN (
	SELECT UserCoverageEntity.user_id
	FROM UserCoverageEntity 
	WHERE UserCoverageEntity.id=UNHEX('11e9e4e9c970a3f4857698fa9b0d2efc')
	) AS c ON c.user_id=UserEntity.id
	)
	OR  UserEntity.id IN (SELECT UserEntity.id FROM UserEntity
INNER JOIN (
	SELECT UserSchemeEntity.user_id
	FROM UserSchemeEntity
	LEFT JOIN SchemeCategoryEntity ON SchemeCategoryEntity.id=UserSchemeEntity.schemeCategory_id
	WHERE SchemeCategoryEntity.scheme_id=UNHEX('11e9ded018e2ac0eac7098fa9b0d2efc')
) AS b ON b.user_id=UserEntity.id)


C: Full table scan > 10s:
SELECT *
FROM UserEntity
WHERE
UserEntity.id IN (
	SELECT UserCoverageEntity.user_id
	FROM UserCoverageEntity 
	WHERE UserCoverageEntity.id=UNHEX('11e9e4e9c970a3f4857698fa9b0d2efc')
)
OR
UserEntity.id IN (
	SELECT UserSchemeEntity.user_id
	FROM UserSchemeEntity
	LEFT JOIN SchemeCategoryEntity ON SchemeCategoryEntity.id=UserSchemeEntity.schemeCategory_id
	WHERE SchemeCategoryEntity.scheme_id=UNHEX('11e9ded018e2ac0eac7098fa9b0d2efc')
)