sorting with Order By in mysql - mysql

I am using mysql as database and i have a table like the one below.
CREATE TABLE IF NOT EXISTS `logins` (
`id` int(255) NOT NULL AUTO_INCREMENT,
`userid` varchar(255) NOT NULL,
`date` varchar(255) NOT NULL,
`status` varchar(255) NOT NULL,
KEY `id` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=346 ;
I want to sort mysql results with order by.The problem is when i use this sql it takes only the first recod of date. Which is an older date. I want the newest date. last login date of user.
SELECT * FROM `logins` WHERE `status`='valid' GROUP BY `userid` ORDER BY `date` DESC
Any suggestions?

To do this you use a sub query to get the latest record for each user id and then join that to the logins table to get the rest of the details
SELECT logins.*
FROM logins
INNER JOIN
(
SELECT userid, MAX(`date`) AS max_date
FROM `logins`
WHERE `status` = 'valid'
GROUP BY `userid`
) sub0
ON logins.userid = sub0.userid
AND logins.`date` = sub0.max_date
WHERE `status` = 'valid'

You almost had it. Assuming id and userId doesn't evolve from one login to another, asking the MAX date should give you the expected result.
SELECT id, userId, MAX(`date`) AS lastDate, 'valid'
FROM `logins`
WHERE `status`='valid'
GROUP BY `userid`
ORDER BY `lastDate` DESC
Please note that you would need a JOIN if there were data that change between logins in the table.

Related

How to get NULL at the top of the sort?

Two tables are defined:
CREATE TABLE `users` (
`user_id` mediumint(6) unsigned NOT NULL AUTO_INCREMENT,
`score` tinyint(1) unsigned DEFAULT NULL,
PRIMARY KEY (`user_id`)
);
CREATE TABLE `online` (
`user_id` mediumint(6) unsigned NOT NULL AUTO_INCREMENT,
`url` varchar(255) NOT NULL,
PRIMARY KEY (`user_id`)
);
How to combine the tables so that the result would be sorted by the score field from the largest to the smallest but at the top there were records with the value NULL?
This query does not sort the second sample:
(SELECT * FROM `online` JOIN `users` USING(`user_id`) WHERE `score` IS NULL)
UNION
(SELECT * FROM `online` JOIN `users` USING(`user_id`) WHERE `score` IS NOT NULL ORDER BY `score` DESC)
Use two keys in the sort:
SELECT *
FROM `online` o JOIN
`users`
USING (user_id)
ORDER BY (`score` IS NULL) DESC, Score DESC;
MySQL treats booleans as numbers in a numeric context, with "1" for true and "0" for false. So, DESC puts the true values first.
Incidentally, your version would look like it works if you used UNION ALL rather than UNION. However, it is not guaranteed that the results are in any particular order unless you explicitly have an ORDER BY.
The UNION incurs overhead for removing duplicates and in doing so rearranges the data.
Try:
select * from online join users using (user_id) order by ifnull(score, 10) desc;
You can use order by Nulls Last in the end of your sql to show nulls on the first.
You can try below -
select * from
(
SELECT *,1 as ord FROM `online` JOIN `users` USING(`user_id`) WHERE `score` IS NULL
UNION
SELECT *,2 FROM `online` JOIN `users` USING(`user_id`) WHERE `score` IS NOT NULL
)A ORDER BY ord asc,`score` DESC

Sqlite alias column give an error

this is my table
CREATE TABLE IF NOT EXISTS `calls` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`date` timestamp NOT NULL,
`type` int(11) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB
and there are data on it its
now i use this query for get type data with same day
SELECT user.name_first calls.date as days, (SELECT GROUP_CONCAT(type) FROM calls WHERE DAY(date) = DAY(days) ) FROM calls JOIN user ON user.user_id = calls.user_id WHERE calls.id IN (SELECT MAX(id) FROM calls GROUP BY DAY(calls.date))
as we see i do this calls.date as days and try to get type for this data by
(SELECT GROUP_CONCAT(type) FROM calls WHERE DAY(date) = DAY(days) )
its work on mysql result in mysql
but when i try it on sqlite its say
no such column: days (code 1): , while compiling
i read sqlite support alias

MysqL big table query optimization

I have a chatting application. I have an api which returns list of users who the user talked. But it takes a long to mysql return a list messages when it reachs 100000 rows of data.
This is my messages table
CREATE TABLE IF NOT EXISTS `messages` (
`_id` int(11) NOT NULL AUTO_INCREMENT,
`fromid` int(11) NOT NULL,
`toid` int(11) NOT NULL,
`message` text NOT NULL,
`attachments` text NOT NULL,
`status` tinyint(1) NOT NULL DEFAULT '0',
`date` datetime NOT NULL,
`delete` varchar(50) NOT NULL,
`uuid_read` varchar(250) NOT NULL,
PRIMARY KEY (`_id`),
KEY `fromid` (`fromid`,`toid`,`status`,`delete`,`uuid_read`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=118561 ;
and this is my users table (simplified)
CREATE TABLE IF NOT EXISTS `users` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`login` varchar(50) DEFAULT '',
`sex` tinyint(1) DEFAULT '0',
`status` varchar(255) DEFAULT '',
`avatar` varchar(30) DEFAULT '0',
`last_active` datetime DEFAULT NULL,
`active` tinyint(1) DEFAULT '1',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=15523 ;
And here is my query (for user with id 1930)
select SQL_CALC_FOUND_ROWS `u_id`, `id`, `login`, `sex`, `birthdate`, `avatar`, `online_status`, SUM(`count`) as `count`, SUM(`nr_count`) as `nr_count`, `date`, `last_mesg` from
(
(select `m`.`fromid` as `u_id`, `u`.`id`, `u`.`login`, `u`.`sex`, `u`.`birthdate`, `u`.`avatar`, `u`.`last_active` as online_status, COUNT(`m`.`_id`) as `count`, (COUNT(`m`.`_id`)-SUM(`m`.`status`)) as `nr_count`, `tm`.`date` as `date`, `tm`.`message` as `last_mesg` from `messages` as m inner join `messages` as tm on `tm`.`_id`=(select MAX(`_id`) from `messages` as `tmz` where `tmz`.`fromid`=`m`.`fromid`) left join `users` as u on `u`.`id`=`m`.`fromid` where `m`.`toid`=1930 and `m`.`delete` not like '%1930;%' group by `u`.`id`)
UNION
(select `m`.toid as `u_id`, `u`.`id`, `u`.`login`, `u`.`sex`, `u`.`birthdate`, `u`.`avatar`, `u`.`last_active` as online_status, COUNT(`m`.`_id`) as `count`, 0 as `nr_count`, `tm`.`date` as `date`, `tm`.`message` as `last_mesg` from `messages` as m inner join `messages` as tm on `tm`.`_id`=(select MAX(`_id`) from `messages` as `tmz` where `tmz`.`toid`=`m`.`toid`) left join `users` as u on `u`.`id`=`m`.`toid` where `m`.`fromid`=1930 and `m`.`delete` not like '%1930;%' group by `u`.`id`)
order by `date` desc ) as `f` group by `u_id` order by `date` desc limit 0,10
Please help to optimize this query
What I need,
Who user talked to (name, sex, and etc)
What was the last message (from me or to me)
Count of messages (all)
Count of unread messages (only to me)
The query works well, but takes too long.
The output must be like this
You have some design problems on your query and database.
You should avoid keywords as column names, as that delete column or the count column;
You should avoid selecting columns not declared in the group by without an aggregation function... although MySQL allows this, it's not a standard and you don't have any control on what data will be selected;
Your not like construction may cause a bad behavior on your query because '%1930;%' may match 11930; and 11930 is not equal to 1930;
You should avoid like constructions starting and ending with % wildcard, which will cause the text processing to take longer;
You should design a better way to represent a message deletion, probably a better flag and/or another table to save any important data related with the action;
Try to limit your result before the join conditions (with a derived table) to perform less processing;
I tried to rewrite your query the best way I understood it. I've executed my query in a messages table with ~200.000 rows and no indexes and it performed in 0,15 seconds. But, for sure you should create the right indexes to help it perform better when the amount of data increase.
SELECT SQL_CALC_FOUND_ROWS
u.id,
u.login,
u.sex,
u.birthdate,
u.avatar,
u.last_active AS online_status,
g._count,
CASE WHEN m.toid = 1930
THEN g.nr_count
ELSE 0
END AS nr_count,
m.`date`,
m.message AS last_mesg
FROM
(
SELECT
MAX(_id) AS _id,
COUNT(*) AS _count,
COUNT(*) - SUM(m.status) AS nr_count
FROM messages m
WHERE 1=1
AND m.`delete` NOT LIKE '%1930;%'
AND
(0=1
OR m.fromid = 1930
OR m.toid = 1930
)
GROUP BY
CASE WHEN m.fromid = 1930
THEN m.toid
ELSE m.fromid
END
ORDER BY MAX(`date`) DESC
LIMIT 0, 10
) g
INNER JOIN messages AS m ON 1=1
AND m._id = g._id
LEFT JOIN users AS u ON 0=1
OR (m.fromid <> 1930 AND u.id = m.fromid)
OR (m.toid <> 1930 AND u.id = m.toid)
ORDER BY m.`date` DESC
;

Cant construct mysql select query without subqueries

I have a table
CREATE TABLE logs(
id INT(11) UNSIGNED NOT NULL AUTO_INCREMENT,
ip INT(11) UNSIGNED NOT NULL,
`date` TIMESTAMP,
`time` INT(11) UNSIGNED NOT NULL,
referrer VARCHAR(255) NOT NULL,
uri VARCHAR(255) NOT NULL,
PRIMARY KEY (id),
)
And I need to fetch following data and group then by IP:
IP
referrer that was first for IP (date is min.)
last visited uri for IP
number of unique uris
Is it possible to write such query without subqueries?
My solution WITH subqueries:
SELECT
`logs`.`ip`,
(SELECT
`tmp`.`referrer`
FROM
`logs` AS `tmp`
WHERE
`tmp`.`ip` = `logs`.`ip`
ORDER BY `tmp`.`date`
LIMIT 1) 'referrer',
(SELECT
`tmp`.`uri`
FROM
`logs` AS `tmp`
WHERE
`tmp`.`ip` = `logs`.`ip`
ORDER BY
`tmp`.`date` DESC
LIMIT 1) 'uri',
COUNT(DISTINCT (`logs`.`uri`)) 'urls'
FROM
`logs`
GROUP BY
`logs`.`ip`
select
`logs`.`ip`,
`tmp`.`referrer`
`tmp`.`uri`
count(distinct `logs`.`uri`)) as `urls`
from `logs`
left join `tmp` on `tmp`.`ip`=`logs`.`ip`
group by `logs`.`ip`
However this doesn't allow for the order by tmp.date part. If it's absolutely required, let me know in a comment and I'll update this code to allow that.

Count passed logins and failed logins in same query?

I have a query that select the top 5 of the UID that most logged in.
I show results like that:
"A name" connected 457 times, failed 124 times
My actual query only get the " 457 " times, I don't know how to select the failed logins in the same query.
I have a field in my database named " passed ". The value is 0 if failed, 1 if correct.
Current query:
SELECT uid, COUNT(uid) AS cnt
FROM logins
GROUP BY uid
ORDER BY cnt DESC
LIMIT 5
Database structure:
CREATE TABLE IF NOT EXISTS `logins` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`uid` int(11) NOT NULL,
`username` varchar(255) NOT NULL,
`ip` varchar(15) NOT NULL,
`time` int(10) NOT NULL,
`passed` int(1) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=1544 ;
Could you please help me to get working that out?
Thanks in advance
SELECT uid, COUNT(uid) AS cnt, COUNT( IF( passed = 0, 1, NULL ) ) AS failed
FROM logins
GROUP BY uid
ORDER BY cnt DESC
LIMIT 5
SELECT uid, COUNT(uid) AS cnt, (SELECT COUNT(uid) FROM logins WHERE passed=0) AS failed ...
You can use an inner select statement to achieve this.