mysql explain slow where on left joined table - mysql

Question

Playing with a mysql and thinking how to solve one thing in the future. I want to retrieve statuses which are posted by my friends (specific user ids) or are posted inside of the group I follow.
CREATE TABLE `status` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`user_id` int(11) NOT NULL,
`status` text COLLATE utf8_unicode_ci NOT NULL,
PRIMARY KEY (`id`),
KEY `IDX_F23501207E3C61F9` (`user_id`)
) ENGINE=InnoDB AUTO_INCREMENT=1567559 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
CREATE TABLE `group_status` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`group_id` int(11) NOT NULL,
PRIMARY KEY (`id`),
KEY `IDX_F23501207E3C61F9` (`group_id`)
) ENGINE=InnoDB AUTO_INCREMENT=1000001 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
I fed both tables with 1M rows.
The query I am running:
SELECT s.id, s.status, gs.group_id
FROM status s
LEFT JOIN group_status gs
ON s.id = gs.id
WHERE
s.user_id IN (55883,122024,442468,846269,903941,980896,192660,20608,525056,563457)
OR gs.group_id IN (78,79,79,80,80,83,84,85,86,87,88,89,89,91,92,92,94,98)
ORDER BY s.id DESC
LIMIT 15
The result:
Question one:
Shouldn't be the extra role like: "using index" instead of "where" ?
Question two:
Why is the response time so slow? 2,3s
Edit after Tim's answer:
The filesort behaviour I guess is normal when using union no?
Why there is 'using where' in the second row of explain? If in the third is 'using where, using index' ?
In case of how many returned rows from selects you think this would get slow?
The union select seems to be super fast but there is only few rows returning each select currently. I will try to select more rows in each select.

Answer 1

Where you have an "OR" on different columns, mysql may use none of your indexes.
Usually we can solve the problem using "UNION" two separate queries with each matching one of the criteria.
SELECT id, status, group_id FROM
(
SELECT s.id, s.status, gs.group_id
FROM status s
LEFT JOIN group_status gs
ON s.id = gs.id
WHERE
s.user_id IN (55883,122024,442468,846269,903941,980896,192660,20608,525056,563457)
UNION
SELECT s.id, s.status, gs.group_id
FROM status s
LEFT JOIN group_status gs
ON s.id = gs.id
WHERE
gs.group_id IN (78,79,79,80,80,83,84,85,86,87,88,89,89,91,92,92,94,98)
) t
ORDER BY id DESC
LIMIT 15
However, in your case, this may NOT help if either query returns large number of records.
Your status column is defined as text, which may cause the file sort. You can check it to a long varchar to see if the filesort goes way. Or try this to avoid worse case scenario:
SELECT ss.id, group_id, ss.status
FROM (
SELECT id, group_id FROM
(
SELECT s.id, gs.group_id
FROM status s
LEFT JOIN group_status gs
ON s.id = gs.id
WHERE
s.user_id IN (55883,122024,442468,846269,903941,980896,192660,20608,525056,563457)
UNION
SELECT s.id, gs.group_id
FROM status s
LEFT JOIN group_status gs
ON s.id = gs.id
WHERE
gs.group_id IN (78,79,79,80,80,83,84,85,86,87,88,89,89,91,92,92,94,98)
) t
ORDER BY id DESC
LIMIT 15
) f
JOIN status ss
ON f.id =ss.id
ORDER BY ss.id