I am kind of new to this whole INDEXING thing, but am loving it so far! Just a quick (possibly very easy) question...I have a very basic query, where I want to select just the 5 most recent comments from the "comments" table. The "id" column is the PRIMARY.
mysql> EXPLAIN SELECT * FROM comments ORDER BY id DESC LIMIT 5;
+----+-------------+----------+-------+---------------+---------+---------+------+-------+-------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+----------+-------+---------------+---------+---------+------+-------+-------+
| 1 | SIMPLE | comments | index | NULL | PRIMARY | 4 | NULL | 19938 | |
+----+-------------+----------+-------+---------------+---------+---------+------+-------+-------+
1 row in set (0.00 sec)
As you can see, it is scanning the entire table...is there any way around this?
UPDATE for SHOW CREATE TABLE comments:
mysql> show create table comments;
+----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| comments | CREATE TABLE `comments` (
`id` int(12) NOT NULL auto_increment,
`post_id` int(12) NOT NULL,
`comm_id` int(11) NOT NULL,
`userid` int(12) NOT NULL,
`name` varchar(30) NOT NULL,
`content` text NOT NULL,
`location` varchar(30) NOT NULL,
`type` enum('Comment','Advice') NOT NULL,
`likes` int(12) NOT NULL,
`dislikes` int(12) NOT NULL,
`datetime` varchar(255) NOT NULL,
`datetimerss` varchar(255) NOT NULL,
`ip` varchar(255) NOT NULL,
PRIMARY KEY (`id`),
KEY `type` (`type`)
) ENGINE=MyISAM AUTO_INCREMENT=20091 DEFAULT CHARSET=latin1 |
+----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
Related
I have a query like
SELECT `table1`.*
FROM `table1`
WHERE `table1`.`table2_id` IN (1,2,6,12,53,666)
and it works more than 20 seconds
Explain looks like:
+----+-------------+--------------------------+------------+-------+-------------------------------------------------------------------------------+----------------------------------+---------+------+-------+----------+-----------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+--------------------------+------------+-------+-------------------------------------------------------------------------------+----------------------------------+---------+------+-------+----------+-----------------------+
| 1 | SIMPLE | table1 | NULL | range | table2_id | table2_id | 4 | NULL | 74778 | 100.00 | Using index condition |
+----+-------------+--------------------------+------------+-------+-------------------------------------------------------------------------------+----------------------------------+---------+------+-------+----------+-----------------------+
Table looks like
CREATE TABLE `table1` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`table2_id` int(11) NOT NULL,
`table3_id` int(11) NOT NULL,
`field1` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
`field2` int(11) NOT NULL DEFAULT '0',
`created_at` datetime NOT NULL,
`updated_at` datetime NOT NULL,
`field3` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `name_of_index_id` (`table3_id`),
KEY `other_name_of_index` (`field2`),
KEY `table2_id` (`table2_id`)
) ENGINE=InnoDB AUTO_INCREMENT=86623178 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
You can use index to fetch the result quickly. But, Indexing will take more space to generate and store in the database. So, if you are fine to utilize speed compare to space, Indexing will be used with following SQL statement.
ALTER TABLE `table1` ADD INDEX(`table2_id`);
This is my query running in one page of my site
SELECT
DISTINCT b.CruisePortID,
b.SailingDates,
b.CruisePortID,
b.ArriveTime,
b.DepartTime,
b.PortName,
b.DayNumber
FROM
cruise_itineraries a,
cruise_itinerary_days b,
cruise_ports c
WHERE
a.ID = b.CruiseItineraryID
AND a.CruisePortID = c.ID
AND a.ID = '352905'
AND b.CruisePortID != 0
GROUP BY b.DayNumber;
while running this query in phpmy admin its take 3.20 sec because of cruise_itineraries had more 300 000 records
I tried indexing also after indexing it show 2.92 sec. Is any possible to reduced query time less .10 sec. Its help my site performance
here details
CREATE TABLE IF NOT EXISTS `cruise_itineraries` (
`cl` int(11) NOT NULL,
`ID` bigint(20) NOT NULL,
`Description` varchar(500) NOT NULL,
`SailingPlanID` varchar(100) NOT NULL,
`VendorID` varchar(100) NOT NULL,
`VendorName` varchar(100) NOT NULL,
`ShipID` varchar(100) NOT NULL,
`ShipName` varchar(100) NOT NULL,
`Duration` int(11) NOT NULL,
`DestinationID` varchar(100) NOT NULL,
`Date` datetime NOT NULL,
`CruisePortID` varchar(100) NOT NULL,
`TradeRestriction` varchar(100) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
CREATE TABLE IF NOT EXISTS `cruise_itinerary_days` (
`cld` int(11) NOT NULL,
`CruiseItineraryID` varchar(100) NOT NULL,
`SailingDates` datetime NOT NULL,
`VendorID` int(11) NOT NULL,
`VendorName` varchar(100) NOT NULL,
`ShipID` int(11) NOT NULL,
`ShipName` varchar(100) NOT NULL,
`SailingPlanID` int(11) NOT NULL,
`PlanName` varchar(100) NOT NULL,
`DayNumber` bigint(20) NOT NULL,
`PortName` varchar(100) NOT NULL,
`CruisePortID` varchar(100) NOT NULL,
`ArriveTime` varchar(100) NOT NULL,
`DepartTime` varchar(100) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
CREATE TABLE IF NOT EXISTS `cruise_ports` (
`cp` int(11) NOT NULL,
`ID` varchar(100) NOT NULL,
`Name` varchar(100) NOT NULL,
`Description` varchar(1000) NOT NULL,
`NearestAirportCode` varchar(100) NOT NULL,
`UNCode` varchar(100) NOT NULL,
`Address` varchar(500) NOT NULL,
`City` varchar(100) NOT NULL,
`StateCode` varchar(100) NOT NULL,
`CountryCode` varchar(100) NOT NULL,
`PostalCode` varchar(100) NOT NULL,
`Phone` varchar(50) NOT NULL,
`Fax` varchar(100) NOT NULL,
`Directions` varchar(1000) NOT NULL,
`Content` varchar(1000) NOT NULL,
`HomePageURL` varchar(100) NOT NULL,
`Longitude` varchar(100) NOT NULL,
`Latitude` varchar(500) NOT NULL,
`CarnivalID` varchar(100) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
ALTER TABLE `cruise_itineraries`
ADD PRIMARY KEY (`cl`),
ADD KEY `ID_2` (`ID`);
ALTER TABLE `cruise_itineraries`
ADD PRIMARY KEY (`cl`),
ADD KEY `ID_2` (`ID`);
ALTER TABLE `cruise_itinerary_days`
ADD PRIMARY KEY (`cld`);
ALTER TABLE `cruise_ports`
ADD PRIMARY KEY (`cp`);
ALTER TABLE `cruise_itineraries`
MODIFY `cl` int(11) NOT NULL AUTO_INCREMENT;
ALTER TABLE `cruise_itinerary_days`
MODIFY `cld` int(11) NOT NULL AUTO_INCREMENT;
ALTER TABLE `cruise_ports`
MODIFY `cp` int(11) NOT NULL AUTO_INCREMENT;
EXPLAIN RESULT:
+----+-------------+-------+------+---------------+------+---------+-------+---------+--------------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+-------+---------+--------------------------------------------------------+
| 1 | SIMPLE | a | ref | ID_2 | ID_2 | 8 | const | 1 | Using index condition; Using temporary; Using filesort |
| 1 | SIMPLE | c | ALL | NULL | NULL | NULL | NULL | 3267 | Using where; Using join buffer (Block Nested Loop) |
| 1 | SIMPLE | b | ALL | NULL | NULL | NULL | NULL | 2008191 | Using where; Using join buffer (Block Nested Loop) |
+----+-------------+-------+------+---------------+------+---------+-------+---------+--------------------------------------------------------+
+----+-------------+-------+------+------------------------------------+------------------------------------+---------+-------+------+--------------------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+------------------------------------+------------------------------------+---------+-------+------+--------------------------------------------------------------+
| 1 | SIMPLE | b | ref | Idx_CruiseItineraryID_CruisePortID | Idx_CruiseItineraryID_CruisePortID | 9 | const | 12 | Using index condition; Using temporary; Using filesort |
| 1 | SIMPLE | a | ref | ID_2 | ID_2 | 8 | const | 1 | Distinct |
| 1 | SIMPLE | c | ALL | NULL | NULL | NULL | NULL | 3267 | Using where; Distinct; Using join buffer (Block Nested Loop) |
+----+-------------+-------+------+------------------------------------+------------------------------------+---------+-------+------+--------------------------------------------------------------+
First I would like to state that try to avoid IMPLICIT MySQL JOINS.
Use INNER JOINS instead.
I personally think the INNER JOIN is better, because it is more
readable. It shows better the relations between the table. You got
those relations in the join, and you do the filtering in the WHERE
clause. This separation makes the query more readable.
The faults I've found:
The data type of cruise_itineraries.ID is BIGINT and the data type of cruise_itinerary_days.CruiseItineraryID is varchar. But you are matching them in a query. So it will run slow no matter if you use index on cruise_itinerary_days.CruiseItineraryID in cruise_itinerary_days table.
Change the data type of cruise_itinerary_days.CruiseItineraryID to BIGINT.
ALTER TABLE cruise_itinerary_days MODIFY CruiseItineraryID BIGINT;
Next you have to create a composite index on cruise_itinerary_days table based on your query.
ALTER TABLE cruise_itinerary_days ADD INDEX Idx_CruiseItineraryID_CruisePortID (CruiseItineraryID, CruisePortID)`
Now create an index in cruise_ports table on cruise_ports.ID field.
ALTER TABLE cruise_ports ADD INDEX Idx_cruise_ports_ID (ID);
And finally the query is formulated using INNER JOINS since I've stated reasons above behind this choice:
SELECT
DISTINCT b.CruisePortID,
b.SailingDates,
b.CruisePortID,
b.ArriveTime,
b.DepartTime,
b.PortName,
b.DayNumber
FROM cruise_itineraries a
INNER JOIN cruise_itinerary_days b ON a.ID = b.CruiseItineraryID
INNER JOIN cruise_ports c ON a.CruisePortID = c.ID
WHERE a.ID = 352905
AND b.CruisePortID != 0
GROUP BY b.DayNumber;
Please refer the table strcuture below.
CREATE TABLE `oarc` (
`ID` bigint(20) NOT NULL AUTO_INCREMENT,
`zID` int(11) NOT NULL,
`cID` int(11) NOT NULL,
`bID` int(11) NOT NULL,
`rtype` char(1) COLLATE utf8_unicode_ci NOT NULL,
`created` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
PRIMARY KEY (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=1821039 ;
Other than the PRIMARY KEY, I have not set any index on this, and when I run the following query
select COUNT(oarc.ID) as total
from `oarc` where`oarc`.`rtype` = 'v'
group
by `oarc`.`zID`
I am getting the result in less than 1 second. But if I add index to zID it is taking more than 5 seconds.
Please see below explain result :
id | select_type | table | type | possible_keys | key | key_len | ref | row | Extra
--------------------------------------------------------------------------------------------------------
1 | SIMPLE | oarc | index | NULL | zone_ID | 4 | NULL | 1909387 | Using where
Currently the table have more than 1821039 records in it and it will increase on a hourly basis. What are the things I need to do in order to reduce the query execution time. I am expecting only something at the table and query level, nothing on my.cnf or server side because I can not do anything there.
Thanks in advance.
Is this better?
CREATE TABLE `oarc` (
`ID` bigint(20) NOT NULL AUTO_INCREMENT,
`zID` int(11) NOT NULL,
`cID` int(11) NOT NULL,
`bID` int(11) NOT NULL,
`rtype` char(1) COLLATE utf8_unicode_ci NOT NULL,
`created` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
PRIMARY KEY (`ID`),
KEY(rtype,zid)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=1821039 ;
explain
select COUNT(oarc.ID) as total
from `oarc` where`oarc`.`rtype` = 'v'
group
by `oarc`.`zID`
+----+-------------+-------+------+---------------+-------+---------+-------+------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+---------------+-------+---------+-------+------+--------------------------+
| 1 | SIMPLE | oarc | ref | rtype | rtype | 3 | const | 1 | Using where; Using index |
+----+-------------+-------+------+---------------+-------+---------+-------+------+--------------------------+
My query is not using any indexes. Query performing full table scan. What can I do to avoid this?
explain select * from
timed_delivery_messages
where start_time <= '06:39'
and end_time > '06:39'
and mode='Active'
and rotation_weight like '%,45,%'
and substr(day_of_week, 2, 1) = 'T'
limit 1;
Explain Plan
+----+-------------+-------------------------+------+---------------+------+---------+------+------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------------------------+------+---------------+------+---------+------+------+-------------+
| 1 | SIMPLE | timed_delivery_messages | ALL | NULL | NULL | NULL | NULL | 22 | Using where |
+----+-------------+-------------------------+------+---------------+------+---------+------+------+-------------+
1 row in set (0.00 sec)
Tables:
mysql> show create table timed_delivery_messages\G
*************************** 1. row ***************************
Table: timed_delivery_messages
Create Table: CREATE TABLE `timed_delivery_messages` (
`row_create` datetime DEFAULT NULL,
`row_mod` datetime DEFAULT NULL,
`rule_id` int(11) NOT NULL,
`start_time` time DEFAULT NULL,
`end_time` time DEFAULT NULL,
`day_of_week` varchar(7) DEFAULT NULL,
`rotation_weight` varchar(50) DEFAULT NULL,
`mode` varchar(10) DEFAULT 'active',
`long_message` varchar(256) DEFAULT NULL,
`short_message` varchar(256) DEFAULT NULL,
PRIMARY KEY (`rule_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
You must create one group index with columns
start_time,
end_time,
mode
And also do experiment to include day_of_week into this index. Maybe it will speed up your system
Why does lean_users show NULL in the ref column? This causes my query to use a temporary table and a filesort later (when I've added more joins)...
14:45:21 (60) > EXPLAIN select * from users u inner join lean_users lu on u.id = lu.user_id;
+----+-------------+-------+--------+---------------+---------+---------+----------------+------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+---------------+---------+---------+----------------+------+-------------+
| 1 | SIMPLE | lu | index | PRIMARY | PRIMARY | 4 | NULL | 358 | Using index |
| 1 | SIMPLE | u | eq_ref | PRIMARY | PRIMARY | 4 | nwa.lu.user_id | 1 | |
+----+-------------+-------+--------+---------------+---------+---------+----------------+------+-------------+
users table
14:45:24 (61) > show create table users;
+-------+-----------------------------------------------------------------------------+
| Table | Create Table |
+-------+-----------------------------------------------------------------------------+
| users | CREATE TABLE `users` (
`id` int(11) NOT NULL auto_increment,
`email` varchar(255) default NULL,
`first_name` varchar(50) NOT NULL,
`last_name` varchar(50) NOT NULL,
`address1` varchar(255) NOT NULL,
`address2` varchar(255) default NULL,
`city` varchar(25) NOT NULL,
`state` mediumint(9) default NULL,
`zip` varchar(10) NOT NULL,
`phone` varchar(20) default NULL,
`country` smallint(6) NOT NULL,
`username` varchar(10) NOT NULL,
`password` varchar(50) default NULL,
`cdate` datetime NOT NULL,
`last_used` timestamp NOT NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP,
`level` varchar(25) default 'user',
PRIMARY KEY (`id`),
) ENGINE=InnoDB AUTO_INCREMENT=38076 DEFAULT CHARSET=utf8 |
+-------+-----------------------------------------------------------------------------+
lean_users table
14:45:40 (62) > show create table lean_users;
+-------------+-----------------------------------------------------------------------------+
| Table | Create Table |
+-------------+-----------------------------------------------------------------------------+
| lean_users | CREATE TABLE `lean_users` (
`user_id` int(11) NOT NULL,
PRIMARY KEY (`user_id`),
CONSTRAINT `lean_users_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------------+-----------------------------------------------------------------------------+
Why does lean_users show NULL in the ref column?
Because this table is leading in the join and you don't filter on any indexed fields.
This means that each record should be read and evaluated.