I have a table with 4 columns: place_id, username, counter, last_checkin
I'm writing a check-in based system and I'm trying to get a query that will give me the "mayor" of each place. The mayor is the one with most check-ins, and if there is more than 1 than the minimum last_checkin wins.
For example, if I have:
place_id, username, counter, last_checkin
123, tom, 3 , 13/4/10
123, jill, 3, 14/4/10
365, bob, 2, 15/4/10
365, alice, 1, 13/4/10
I want the result to be:
123, tom
365, bob
I'm using it in PHP code
Here is the test data:
CREATE TABLE `my_table` ( `place_id` int(11), `username` varchar(50), `counter` int(11), `last_checkin` date);
INSERT INTO `my_table` VALUES (123,'tom',3,'2010-04-13'),(123,'jill',3,'2010-04-14'),(365,'bob',2,'2010-04-15'),(365,'alice',1,'2010-04-13');
How about..
SELECT
place_id,
(SELECT username
FROM my_table MT2
WHERE MT2.place_id = MT1.place_id
ORDER BY counter DESC, last_checkin ASC
LIMIT 1) AS mayor
FROM my_table MT1
GROUP BY place_id;
Edited as Unreason suggests to have ascending order for last_checkin.
Brian's correlated query is something I would write. However I found this different take and it might perform differently depending on the data
SELECT
mt1.place_id,
mt1.username
FROM
my_table mt1 LEFT JOIN my_table mt2
ON mt1.place_id = mt2.place_id AND
(mt1.counter < mt2.counter OR
(mt1.counter = mt2.counter AND mt1.last_checkin > mt2.last_checkin)
)
WHERE
mt2.place_id IS NULL
Which uses left join to get to the top records according to certain conditions.
$data = query("SELECT max(counter) counter,username FROM table GROUP By place_id ORDER By last_checkin DESC");
Related
I have 3 tables:
event_timestamps with colums Race_number, timestamp
event_entry with Race_number, User_id
user with user_id, Firstname, lastname
I want to find race_numbers that are not linked to a user_id, and count laps while I'm at it by Joining event_timestamps and event_entry.
select event_entry.user_id, max(timestamp), event_timestamps.race_number, count(event_timestamps.race_number)
from event_timestamps
left join event_entry on event_timestamps.race_number = event_entry.race_number and event_entry.event_id=430
where timestamp > '2022-05-28 11:50:00' and timestamp < '2022-05-29'
group by event_timestamps.race_number
order by count(event_timestamps.race_number) desc , max(timestamp);
Output
user_id
max(timestamp)
race_number
count(event...)
NULL
2022-05-28 12:30:01
1000
5
14694
2022-05-28 12:30:02
32
5
37617
2022-05-28 12:30:17
44
5
16134
2022-05-28 12:34:37
24
5
But when I join tbl.user the Null value disappears. I want to display the NULL so I can see if we are missing user data.
This query sort of works but the NULL value is not displaying:
select user.firstname, user.lastname, max(timestamp), event_timestamps.race_number, count(event_timestamps.race_number)
from event_timestamps
left join event_entry on event_timestamps.race_number = event_entry.race_number
inner join user on user.user_id = event_entry.user_id
where timestamp > '2022-05-28 11:50:00' and timestamp < '2022-05-29' and event_entry.event_id=430
group by event_timestamps.race_number
order by count(event_timestamps.race_number) desc , max(timestamp);```
firstname
lastname
max(timestamp)
race_number
count(event....)
Albert
Coles
12:30:02
32
5
Vince
Butre
12:30:17
44
5
John
Plessis
12:34:37
24
5
So I want race_number 1000 (for example) to display as well with NULL values in firstname, lastname.
Any assistance would be much appreciated because this is breaking my novice brain!
The events_timestamps has multiple occurances of the same race_number as the user completes laps. We count the laps and creat rank by using the last lap time (MAX timestamp) and sorting from there.
Try it like this:
SELECT user.firstname, user.lastname, s.timestamp, s.race_number, s.user_id, s.count
FROM (
SELECT event_entry.user_id as user_id, max(timestamp) as timestamp, event_timestamps.race_number as race_number, count(event_timestamps.race_number) as count
from event_timestamps
Left join event_entry on event_timestamps.race_number = event_entry.race_number and event_entry.event_id=430
Where timestamp > '2022-05-28 11:50:00' and timestamp < '2022-05-29'
group by event_timestamps.race_number, event_entry.user_id
) s
LEFT JOIN user on user.user_id = s.user_id
order by s.count desc , s.timestamp
like #Marshal_c said, inner join doesn't work, cause it gets rid of NULLs, viz. SQL JOIN and different types of JOINs
also like #Honk_der_Hase points out, your code is missing group by for all columns. When your SQL works, i asume, that you work in MariaDB, which takes in this case first found element (equivalent of ORALCE's TOP())
In your scenario, you should also have some kind of integrity rule, which will prevent from having multiple users (user_id) with same race number (race_number). If you had thouse records in your database, the rows would start duplicating.
Also be aware, that some databases (like MariaDB) can have problems with table called user because table named like that is used for authentication into database (in information_scheme)
I have been struggling to set this up for months and months!
I need help with setting rank to my database.
This is how my current code looks like:
$db->queryNoReturn("SET #a:=0");
return $db->query("
SELECT * FROM
(SELECT
`FFA_Stats`.`id`,
`FFA_Stats`.`player_uuid`,
`FFA_Stats`.`points`,
`FFA_Stats`.`hits`,
`FFA_Stats`.`shots`,
`FFA_Stats`.`wins`,
`FFA_Stats`.`tkills`,
`FFA_Stats`.`tdeaths`,
(`FFA_Stats`.`tkills`/`FFA_Stats`.`tdeaths`) as `KDR`,
`player`.`name`,
`player`.`uuid`,
`player`.`online`,
(#a:=#a+1) AS rank
FROM `FFA_Stats`
INNER JOIN `player` ON `FFA_Stats`.`player_uuid`=`player`.`uuid`
ORDER BY `points` DESC
) AS `sub`
");
Basically its sorting it by points and you can check how it looks like here: http://filipvlaisavljevic.com/clash/ffa.php
All I want to do is add rank to the sorted table so the player with the most points would be #1 etc.
Does anyone know what to do?
Usually a rank number would be an integer that you could generate from iterating through the rows of the query result. eg. echo $count++;
If you have calculated or attributed a rank in your database then you can add 'order by' statements separated by commas. eg.
FROM `FFA_Stats`
INNER JOIN `player`
ON `FFA_Stats`.`player_uuid`=`player`.`uuid`
ORDER BY `rank` DESC, `points` DESC) AS `sub`
");
so I'm trying to create a ranking system for my website, however as a lot of the records have same number of points, they all have same rank, is there a way to avoid this?
currently have
$conn = $db->query("SELECT COUNT( * ) +1 AS 'position' FROM tv WHERE points > ( SELECT points FROM tv WHERE id ={$data['id']} )");
$d = $db->fetch_array($conn);
echo $d['position'];
And DB structure
`id` int(11) NOT NULL,
`name` varchar(150) NOT NULL,
`points` int(11) NOT NULL,
Edited below,
What I'm doing right now is getting records by lets say
SELECT * FROM tv WHERE type = 1
Now I run a while loop, and I need to make myself a function that will get the rank, but it would make sure that the ranks aren't duplicate
How would I go about making a ranking system that doesn't have same ranking for two records? lets say if the points count is the same, it would order them by ID and get their position? or something like that? Thank you!
If you are using MS SQL Server 2008R2, you can use the RANK function.
http://msdn.microsoft.com/en-us/library/ms176102.aspx
If you are using MySQL, you can look at one of the below options:
http://thinkdiff.net/mysql/how-to-get-rank-using-mysql-query/
http://www.fromdual.ch/ranking-mysql-results
select #rnk:=#rnk+1 as rnk,id,name,points
from table,(select #rnk:=0) as r order by points desc,id
You want to use ORDER BY. Applying on multiple columns is as simple as comma delimiting them: ORDER BY points, id DESC will sort by points and if the points are the same, it will sort by id.
Here's your SELECT query:
SELECT * FROM tv WHERE points > ( SELECT points FROM tv WHERE id ={$data['id']} ) ORDER BY points, id DESC
Documentation to support this: http://dev.mysql.com/doc/refman/5.0/en/sorting-rows.html
Many Database vendors have added special functions to their products to do this, but you can also do it with straight SQL:
Select *, 1 +
(Select Count(*) From myTable
Where ColName < t.ColName) Rank
From MyTable t
or to avoid giving records with the same value of colName the same rank, (This requires a key)
Select *, 1 +
(Select Count(Distinct KeyCol)
From myTable
Where ColName < t.ColName or
(ColName = t.ColName And KeyCol < t.KeyCol)) Rank
From MyTable t
I have a table that is is sorted 1st by Reminder Date then ID
Table Looks like:
ID | remind_date
1 2011-01-23
2 2010-02-21
4 2011-04-04
5 2011-04-04
6 2009-05-04
I am using a PHP front end to move forward and back thur the records. I want to have forward and back buttons but i am running into a problem with the 2 reminder dates that are the same.
Just to note the ID's are NOT in order, they are here but in the actual database they are mixed up when sorting by reminder_date
The select statement i am using is: ($iid is the current record i am on)
SELECT id FROM myDB.reminders where remind_date > (SELECT remind_date FROM myDB.reminders where id=$iid) order by remind_date ASC LIMIT 1
So what happens when i get to the dates that are the same its skips over one because its asking for remind_date >.
If i use remind_date >= it returns the current record. My solution was then to use limit 2 and check via PHP to if the 1st record = my current ID, if it did use the next one. but what it there are 3 dates the same or 4 etc..
I also thought about using the ID field but since they are out of order i can't add in a ID > $iid.
Any ideas? it works great except for 2 dates that are the same.
You might be able to use this:
SELECT ID, remind_date
FROM
(
SELECT #prev_id := -1
) AS vars
STRAIGHT_JOIN
(
SELECT
ID,
remind_date,
#prev_id AS prev_id,
#prev_id := id
FROM myDB.reminders
ORDER BY remind_date, ID
) T1
WHERE prev_id = $iid
Here is a test of the above with your test data from your comment:
CREATE TABLE Table1 (ID INT NOT NULL, remind_date DATE NOT NULL);
INSERT INTO Table1 (ID, remind_date) VALUES
(45, '2011-01-14'),
(23, '2011-01-22'),
(48, '2011-01-23'),
(25, '2011-01-23'),
(63, '2011-02-19');
SELECT ID, remind_date
FROM
(
SELECT #prev_id := -1
) AS vars
STRAIGHT_JOIN
(
SELECT
ID,
remind_date,
#prev_id AS prev_id,
#prev_id := id
FROM table1
ORDER BY remind_date, ID
) T1
WHERE prev_id = 25
Result:
ID remind_date
48 2011-01-23
add a condition WHERE ID<>MY_LAST_ID. This can not work with triple and more same dates, so you can collect already taken ID's to array like (4,5,6) - see array_push(), implode it with "," to convert to a string (let's call it YOUR_IDS_STRING) and add to your query:
WHERE id NOT IN( YOUR_IDS_STRING )
And after each query make check, does date has changed and if it does - you can unset your array and start from begining (this is not neccesary, but gives you more performance, because YOUR_ID_STRING will be only that long as is need).
If your page is refreshing between queries, maybe try to push YOUR_ID_STRING in session variable, _GET or cookies, and simply concat next id's by operator .=
I used the code provided by Mark Byers and with small changes I adapted it to navigate in opposite directions (and to pass other columns too, not only the date and ID):
$results = $mysqli->query("SELECT * FROM (SELECT #prev_id := -1) AS vars STRAIGHT_JOIN (SELECT *, #prev_id AS prev_id, #prev_id := ID FROM my_table ORDER BY data, ID) T1 WHERE prev_id = ".$ID);
$results = $mysqli->query("SELECT * FROM (SELECT #next_id := 1) AS vars STRAIGHT_JOIN (SELECT *, #next_id AS next_id, #next_id := ID FROM my_table ORDER BY data DESC, ID DESC) T1 WHERE next_id = ".$ID);
I tested it on duplicate dates and it navigates well trough a list of records displayed with:
$results = $mysqli->query("SELECT * FROM my_table ORDER BY data DESC, ID DESC");
Hello i have a question on picking random entries from a database. I have 4 tables, products, bids and autobids, and users.
Products
-------
id 20,21,22,23,24(prime_key)
price...........
etc...........
users
-------
id(prim_key)
name user1,user2,user3
etc
bids
-------
product_id
user_id
created
autobids
--------
user_id
product_id
Now a multiple users can have an autobid on an product. So for the next bidder I want to select a random user from the autobid table
example of the query in language:
for each product in the autobid table I want a random user, which is not the last bidder.
On product 20 has user1,user2,user3 an autobidding.
On product 21 has user1,user2,user3 an autobidding
Then I want a resultset that looks for example like this
20 – user2
21 – user3
Just a random user. I tried miximg the GOUP BY (product_id) and making it RAND(), but I just can't get the right values from it. Now I am getting a random user, but all the values that go with it don't match.
Can someone please help me construct this query, I am using php and mysql
The first part of the solution is concerned with identifying the latest bid for each product: these eventually wind up in temporary table "latest_bid".
Then, we assign randon rank values to each autobid for each product - excluding the latest bid for each product. We then choose the highest rank value for each product, and then output the user_id and product_id of the autobids with those highest rank values.
create temporary table lastbids (product_id int not null,
created datetime not null,
primary key( product_id, created ) );
insert into lastbids
select product_id, max(created)
from bids
group by product_id;
create temporary table latest_bid ( user_id int not null,
product_id int not null,
primary key( user_id, product_id) );
insert into latest_bid
select product_id, user_id
from bids b
join lastbids lb on lb.product_id = b.product_id and lb.created = b.created;
create temporary table rank ( user_id int not null,
product_id int not null,
rank float not null,
primary key( product_id, rank ));
# "ignore" duplicates - it should not matter
# left join on latest_bid to exclude latest_bid for each product
insert ignore into rank
select user_id, product_id, rand()
from autobids a
left join latest_bid lb on a.user_id = lb.user_id and a.product_id = lb.product_id
where lb.user_id is null;
create temporary table choice
as select product_id,max(rank) choice
from rank group by product_id;
select user_id, res.product_id from rank res
join choice on res.product_id = choice.product_id and res.rank = choice.choice;
You can use the LIMIT statement in conjunction with server-side PREPARE.
Here is an example that selects a random row from the table mysql.help_category:
select #choice:= (rand() * count(*)) from mysql.help_category;
prepare rand_msg from 'select * from mysql.help_category limit ?,1';
execute rand_msg using #choice;
deallocate prepare rand_msg;
This will need refining to prevent #choice becoming zero, but the general idea works.
Alternatively, your application can construct the count itself by running the first select, and constructing the second select with a hard-coded limit value:
select count(*) from mysql.help_category;
# application then calculates limit value and constructs the select statement:
select * from mysql.help_category limit 5,1;