How I can optimize query with where index? - mysql

Question

I have query
select `price`, `asset_id`
from `history_average_pairs`
where `currency_id` = 1
and date(`created_at`) >= DATE_SUB(NOW(), INTERVAL 7 DAY)
group by hour(created_at), date(created_at), asset_id
order by `created_at` asc
And table
CREATE TABLE IF NOT EXISTS history_average_pairs (
id bigint(20) unsigned NOT NULL,
asset_id bigint(20) unsigned NOT NULL,
currency_id bigint(20) unsigned NOT NULL,
market_cap bigint(20) NOT NULL,
price double(20,6) NOT NULL,
volume bigint(20) NOT NULL,
circulating bigint(20) NOT NULL,
change_1h double(8,2) NOT NULL,
change_24h double(8,2) NOT NULL,
change_7d double(8,2) NOT NULL,
created_at timestamp NOT NULL DEFAULT current_timestamp(),
updated_at timestamp NOT NULL DEFAULT current_timestamp() ON UPDATE current_timestamp(),
total_supply bigint(20) unsigned NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
ALTER TABLE history_average_pairs
ADD PRIMARY KEY (id),
ADD KEY history_average_pairs_currency_id_asset_id_foreign (currency_id,asset_id),
ALTER TABLE history_average_pairs
MODIFY id bigint(20) unsigned NOT NULL AUTO_INCREMENT;
It contains more than 10 000 000 rows, and query takes
Showing rows 0 - 24 (32584 total, Query took 27.8344 seconds.)
But without currency_id = 1, it takes like 4 sec.
UPDATE 1
Okey, I updated key from currency_id, asset_id to currency_id, asset_id, created_at and it takes
Showing rows 0 - 24 (32784 total, Query took 6.4831 seconds.)
Its much faster, any proposal to do it more faster?
GROUP BY here to take only first row for every hour.
For example:
19:01:10
19:02:14
19:23:15
I need only 19:01:10

Answer 1

You can rephrase the filtering predicate to avoid using expressions on columns. For example:
select max(`price`) as max_price, `asset_id`
from `history_average_pairs`
where `currency_id` = 1
and created_at >= date_add(curdate(), interval - 7 day)
group by hour(created_at), date(created_at), asset_id
order by `created_at` asc
Then, this query could be much faster if you added the index:
create index ix1 on `history_average_pairs` (`currency_id`, created_at);

Answer 2

You must make the test "sargeable"; change
date(`created_at`) >= DATE_SUB(NOW(), INTERVAL 7 DAY)
to
created_at >= CURDATE() - INTERVAL 7 DAY
Then the optimal index is
INDEX(currency_id, -- 1st because of "=" test
created_at, -- 2nd to finish out WHERE
asset_id) -- only for "covering"
When designing an index, it is usually best to handle the WHERE first.
The GROUP BY cannot use the index. Did you really want the hour first?
"I need only 19:01:10" is unclear, so I have not factored that in. Where's the date? Where's the asset_id? See "only_full_group_by". Do you need "groupwise max"?
Making the ORDER BY have the same columns as the GROUP BY avoids a sort. (In your query, the order may be slightly different, but it probably does not matter.)
Datatype issues...
BIGINT takes 8 bytes; INT takes only 4 bytes and is usually big enough. Shrinking the table provides some speed.
double(8,2) takes 8 bytes -- Don't use (m,n) on FLOAT or DOUBLE; it adds an extra rounding. Perhaps you meant DECIMAL(8,2), which takes 4 bytes.