MySQL - Full Text Search - Losing index - php

Question

So here is the scenario:
MySQL
have 1 MYISAM Table
colum named v.value has a full text index
Basic query works fine, uses the index as expected:
SELECT p.online_identifier
FROM (...)
WHERE r.area_id = 3 AND s.state_id= 4
AND (snap.area_has_catalogues_attributes_id = 7028
AND MATCH (v.value) AGAINST('+SomeBrand' IN BOOLEAN MODE))
Now when I add an OR, the full text search index (on v.value) is not used.
I run Explain to verify it.
The query would look something like this:
(...)
WHERE r.area_id = 3 AND s.state_id= 4 AND
(snap.area_has_catalogues_attributes_id = 7028 AND MATCH (v.value) AGAINST('+SomeBrand' IN BOOLEAN MODE))
OR (snap.area_has_catalogues_attributes_id = 7045 AND MATCH (v.value) AGAINST('+OtherBrand' IN BOOLEAN MODE))
I dont understand why.
Any ideas?

Answer 1

Here is something interesting: The query you have is actually causing the FULLTEXT indexing to be ignored. Don't worry, it is not your fault. I wrote about this before : Is there a way to hint to query optimizer to MySQL which constraints should be done first?
After looking over my answer and its subsequent links, now let's look at your original query:
SELECT p.online_identifier
FROM (...)
WHERE r.area_id = 3 AND s.state_id= 4
AND (snap.area_has_catalogues_attributes_id = 7028
AND MATCH (v.value) AGAINST('+SomeBrand' IN BOOLEAN MODE))
You will have to execute the FULLTEXT search alone and retrieve IDs only.
Use those IDs to join to the other table aliases.
Let me take a query from one of my other links to demonstrate what to do to your query
Instead of this query
select * from seeds WHERE MATCH(text) AGAINST
("mount cameroon" IN BOOLEAN MODE) = 4;
you must refactor it into something like this:
SELECT B.* FROM
(
SELECT id,MATCH(text) AGAINST
("mount cameroon" IN BOOLEAN MODE) score
FROM seeds
WHERE MATCH(text) AGAINST
("mount cameroon" IN BOOLEAN MODE)
) A
INNER JOIN seeds B USING (id)
WHERE A.score = 4;
Give it a Try !!!