Why is MySQL not using the indexes I have created? - mysql

Question

Any ideas why index is not using on table SD and how to fix it?
I tried to remove the group and sort clauses but still same issue and cant find that is the problem
P.S. dont read this system wont let me post because code is more than description
Query
SELECT sd.filter_group_id, fgd.name AS group_name, sdc.filter_id AS filter_id, fd.name,
COUNT(DISTINCT p2c.product_id) AS total, f.sort_order, sd.sort_order AS sort,
(CASE
WHEN fgd.custom_order = 1
THEN COUNT(p2c.product_id)
END) AS custom_order
FROM oc_sd_filter sd
JOIN oc_product_to_category p2c ON p2c.category_id = sd.category_id
JOIN oc_product_filter sdc18 ON sdc18.product_id = p2c.product_id
JOIN oc_product_filter sdc21 ON sdc21.product_id = p2c.product_id
JOIN oc_product p ON p.product_id = p2c.product_id
JOIN oc_product_filter sdc ON sdc.product_id = p2c.product_id
JOIN oc_filter f ON sdc.filter_id = f.filter_id
JOIN oc_filter_description fd ON sdc.filter_id = fd.filter_id
JOIN oc_filter_group_description fgd ON fd.filter_group_id = fgd.filter_group_id
WHERE sd.category_id = '93'
AND p.status = '1'
AND sd.filter_group_id = fd.filter_group_id
AND sd.status = 1
AND sdc18.filter_id IN (199,200,120,321,611,451,380,542)
AND sdc21.filter_id IN (241,242)
GROUP BY fd.filter_id, fd.filter_group_id
ORDER BY sd.sort_order ASC,
(CASE
WHEN fgd.custom_order = 0
THEN f.sort_order
END) ASC,
(CASE
WHEN fgd.custom_order = 1
THEN COUNT(p2c.product_id)
END) DESC
EXPLAIN
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE sd ALL filter,cat,status NULL NULL NULL 11 Using where; Using temporary; Using filesort
1 SIMPLE fgd ref PRIMARY,filter_group_id PRIMARY 4 example_db.sd.filter_group_id 1
1 SIMPLE p2c ref PRIMARY,category_id, category_id 4 example_db.sd.category_id 59 Using index
1 SIMPLE p eq_ref PRIMARY,status,product_id PRIMARY 4 example_db.p2c.product_id 1 Using where
1 SIMPLE sdc ref PRIMARY PRIMARY 4 example_db.p2c.product_id 9 Using index
1 SIMPLE fd ref PRIMARY,filter PRIMARY 4 example_db.sdc.filter_id 1 Using where
1 SIMPLE f eq_ref PRIMARY PRIMARY 4 example_db.sdc.filter_id 1
1 SIMPLE sdc21 ref PRIMARY PRIMARY 4 example_db.p2c.product_id 9 Using where; Using index
1 SIMPLE sdc18 ref PRIMARY PRIMARY 4 example_db.p2c.product_id 9 Using where; Using index
Table
CREATE TABLE `oc_sd_filter` (
`id` int(11) NOT NULL,
`category_id` int(11) NOT NULL,
`filter_group_id` int(11) NOT NULL,
`status` int(11) NOT NULL,
`sort_order` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
--
-- Indexes for table `oc_sd_filter`
--
ALTER TABLE `oc_sd_filter`
ADD PRIMARY KEY (`id`),
ADD KEY `filter` (`filter_group_id`),
ADD KEY `cat` (`category_id`),
ADD KEY `status` (`status`),
ADD KEY `sort_order` (`sort_order`);

Answer 1

Suggested composite indexes:
sd: INDEX(category_id, status, filter_group_id, sort_order)
fgd: INDEX(filter_group_id, name, custom_order)
sdc: INDEX(product_id, filter_id)
fd: INDEX(filter_group_id, filter_id, name)
p2c: INDEX(category_id, product_id)
f: INDEX(filter_id, sort_order)
oc_product_filter: INDEX(product_id, filter_id)
p: INDEX(status, product_id)
When adding a composite index, DROP index(es) with the same leading columns.
That is, when you have both INDEX(a) and INDEX(a,b), toss the former.
If that does not help enough, come back and we can talk about turning the query inside out -- so that the GROUP BY is done before most of the JOINs. But first, how many rows in the resultset? How many rows if you take out the GROUP BY clause?
Example (from Comment):
SELECT filter_group_id
FROM sd
WHERE status = 1
ORDER BY sort_order
The Optimal index is both composite and "covering"; the order is important:
INDEX(status, sort_order, filter_group_id)
Any longer index starting with those is essentially "as good". Any shorter index (eg, INDEX(status, sort_order) or starting with that) will be "good", but "not as good".
In particular, the 4-column index I provided above is not useful. It is OK to add both indexes; the Optimizer will decide which index to use for each SELECT.