Could you guys please tell me how to show all online people on the top and all offline after, both lists in ascending order of the username just like Skype does.
My MySQL table is Users, and the columns are as follow:
ID
Username
Last_logged_in - is with unix_timestamp();
the code I am using to show online people is as follow:
select * from users where Last_logged_in >= UNIX_TIMESTAMP() - 60;
and the code I tried was like so:
select id, username, last_logged_in from users where last_logged_in >= UNIX_TIMESTAMP() - 60 UNION select id, username, last_logged_in from users where last_logged_in <= UNIX_TIMESTAMP() - 60 LIMIT 10;
some helps will be really appreciated.
Your query doesn't provide the results you expect because UNION does not preserve the order of the rows from the queries it unions.
You need to enclose each of the unioned queries into parentheses and add ORDER BY after the last query. However, if you do that you obtain a big and slow query that selects all the records from table users in a convoluted way.
The solution is to order the rows descending by column Last_logged_in. This way, the users that logged in recently are returned first. Also you need to add in the fields list the expression that tells if the user is still online. Finally, because your query does not filter the returned users, a LIMIT clause is recommended; otherwise the query will return the entire table which is probably not what you want.
Update
As the OP specified in a comment, the users must be sorted by their online status (online first) and then by their usernames (ascending).
The (updated) query is:
SELECT u.*, IF(Last_logged_in >= UNIX_TIMESTAMP() - 60, 1, 0) as isOnline;
FROM users u
ORDER BY isOnline DESC, username ASC
LIMIT 20
No need for union, just order by the last_logged_in field descending, since you use this field to calculate if a user is logged in or not:
select * from users order by Last_logged_in desc limit 10;
This way the logged in users will be on the top of the list because they loggen in most recently.
UPDATE
Still no need for union if you want to order both lists by username, let's build on axiac's proposed solution:
SELECT u.*, IF(Last_logged_in >= UNIX_TIMESTAMP() - 60, 1, 0) as isOnline;
FROM users u
ORDER BY isOnline DESC, u.Username ASC
Related
First I am new to SQL and PHP.
I have created a simple social networking web app so users can post and follow others to see new posts from them.
At home page a user can first see posts from all users he is followong.
but what i want is to make the user see some other random popular posts that will be ordered by Likes.
here what i have done to get posts from users i follow:
SELECT * FROM posts WHERE author_id in
(SELECT followedID FROM follows WHERE
followerID=:myID)
ORDER BY id DESC LIMIT 10
Now let's say you are following only 1 person. and that person has only one post. here you will see no more than a post!
That's why i want to show more posts when a user has already seen all posts.
i want some easy way to get other posts when the above query has done getting some specific posts.
This is the next query i'd like to execute.
SELECT * FROM posts ORDER BY post_likes DESC LIMIT 10
I wouldn't recommend union, because it incurs overhead for removing duplicates.
Instead, you can use a LEFT JOIN:
SELECT p.*
FROM posts p LEFT JOIN
follows f
ON p.author_id = f.follows_id AND
f.followerID = :myID
ORDER BY (f.follows_id IS NOT NULL) DESC,
(CASE WHEN f.follows_id IS NOT NULL THEN p.id END),
p.post_likes DESC
LIMIT 10;
The ORDER BY puts the followed posts first. The other two clauses order each of the groups by the criteria you want.
You may use UNION to do what you want
(SELECT * FROM posts WHERE author_id in
(SELECT followedID FROM follows WHERE
followerID=:myID)
ORDER BY id DESC limit 0,10)
union
(SELECT * FROM posts ORDER BY post_likes DESC limit 0,10)
LIMIT 0, 10
UNION will automatically append the 2nd query result to the 1st query result, and then show only the number of records specified by the LIMIT clause
Please note that union works only if the queries are of the same structure (which in this case is positive)
Please note that the use of parenthesis is mandatory if you use order by or limit or both
I have used 3 limit clauses (one for each query , and one for the final result of union) AND Both queries have ORDER BY clause. This is to make sure that the records extracted are what you want. (to show the followed posts first, and both are ordered properly)
So I have two tables that displays values like a Facebook look-a-like feed. They both have a datetime column named date, but I want them to order them together by date DESC.
I think join is the correct way(?), but not quite sure. Can someone help me out?
Currently I have them in two different queries:
$status1 = "1";
$stmt1 = $link->prepare('
SELECT id
, ident_1
, ident_2
, date
, ident_1_points
, ident_2_points
FROM duel
WHERE active=?
ORDER
BY date
');
$stmt1-> bind_param('s', $status1);
and
$status2 = "OK";
$stmt2 = $link->prepare('SELECT id, ident, pp, date FROM sales WHERE status=? AND team IN (2, 3) ORDER BY date DESC LIMIT 20');
$stmt2->bind_param('s', $status2);
How should I do this?
If you want one continuous list containing data from both tables, and the whole thing ordered by date overall, then you might need a UNION query in a subquery, and then order the outer query, something like this:
SELECT *
FROM
(
SELECT id, ident_1, ident_2, date, ident_1_points, ident_2_points
FROM duel
WHERE active=?
UNION ALL
SELECT id, ident, pp, date, NULL, NULL
FROM sales
WHERE status=?
AND team IN (2, 3)
LIMIT 20
) list
ORDER BY date DESC
The requirement isn't 100% clear to be honest from your description (sample data and expected results always helps when asking SQL questions), but I think this is pretty close to what you need.
JOIN doesn't seem appropriate, unless you want a result set where items from each table are linked to each other by some common field, and you combine them such that you get all the columns side by side, showing the data from one table next to the data which matches from the other table.
If you're unsure, I suggest looking at tutorials / examples / documentation which show what JOIN does, and what UNION does.
Using this query,
SELECT username, MAX(wordpermin) as maxword,date_created FROM user_records where DATE(date_created) = CURDATE() GROUP BY(username) ORDER BY maxword DESC LIMIT 20
I am trying to query a limit of 20 of the top wordpermin by their username and the time created and that by calling date_created in the current 24 hours.
The problem I have is when I have a new high wordpermin. Instead of giving me also the new date_created, it keeps the old value of date_created. I even looked into my database and I made sure I have date_created updated. How can this happen?
I mean, I have two values from different rows.
The following query gives you the last date where a user has the maxword.
Your query would not run when you activated ONLY_FULL_GROUP_BY.
You should always specify for every column which aggregation function you want to use, because SQL rows don't have any order and every column will be selected on its own.
I selected Max (date_created), so that MySQL knows which date to show, because if there were more than one date with the same maximum word, MySQL would show all.
SELECT
u.username, u1.maxword, MAX(u.date_created)
FROM
user_records u
INNER JOIN
(SELECT
username,DATE(date_created) date_created, MAX(wordpermin) AS maxword
FROM
user_records
GROUP BY username,DATE(date_created)) u1 ON u.username = u1.username
AND u.wordpermin = u1.maxword AND Date(u.date_created) = DATE(u1.date_created)
WHERE
DATE(u.date_created) = CURDATE()
GROUP BY (username)
ORDER BY maxword DESC
LIMIT 20;
LIMIT 20
Examole http://sqlfiddle.com/#!9/857355/2
I am looking for an SQL statement that returns users rank by score, but does so in order, which is not happening with the code below:
$sql = "SELECT COUNT(*) AS rank FROM users WHERE points>=(SELECT points FROM users WHERE uid='$uid')";
Instead, each user has the same rank depending on how many users there are. So if there are 25 users, each of their ranks will display as 25 but this is not actually the case, as surely there must be an individual rank for each user.
I have tried a couple of different of different solutions, but I can't quite put the logic together. I thought this would work:
$sql ="SELECT COUNT(*)-1 AS rank FROM users WHERE points>=(SELECT points FROM users WHERE uid='$uid' ORDER BY DESC)";
But I've had no success.
TLDR; How could I change my SQL statement to reflect users rank in order by score, without multiple users having the same rank?
If you are trying to order the data in the table using the points and give them individual rank you can use ROW_NUMBER()
SELECT *,ROW_NUMBER() OVER (ORDER BY points DESC) AS RANK FROM users
ROW_NUMBER() is not available in MYSQL. You can do following for MYSQL
SELECT
#r:=#r+1 Rank,tbl.*
FROM users tbl, (select #r:=0) as r
ORDER BY users.points DESC;
Consider you have data
Points
3
7
8
Using Select statement with ROW_NUMBER() you will get result as follows
Result:
Points Rank
8 1
7 2
3 3
My search query runs like:
select * from posts p where p.post like '%test%' ORDER BY p.upvotes DESC,
p.unix_timestamp DESC LIMIT 20
If there are more than 20 results for the searched keyword, i find out the minimum timestamp value, store it in a hidden element and run another query to Load More results like:
select * from posts p where p.post like '%test%' and p.unix_timestamp < 1360662045
ORDER BY p.upvotes DESC, p.unix_timestamp DESC LIMIT 20
Whats really happening is that my first query is ignoring (Obviously, my mistake) posts which haven't had any votes(meaning 0 votes) because of my ORDER BY p.upvotes DESC and as a result of this, i noticed that it fetched the first post in the table in the first 20 results, so the minimum timestamp becomes first post's timestamp. Now after this, if i try to fetch the next 20 results which is less than the minimum timestamp, it doesn't give anything.
Right now, i am simply using the upvotes ordering to fetch top records. Should i be using some algorithm like Bayesian Average or some other algorithm?
Please advise how i can improve the queries if i had to stay with current system of ordering or is there any viable and more efficient method i should be using?
P.S. If possible, please refer some resources about the Bayesian Average(it seems to be most used) or some other alternative?
Storing the timestamp when you first do a search and then using that for the next query you could use something like this:-
$sql = "SELECT *
FROM posts p
LEFT OUTER JOIN (SELECT post_id, COUNT(*) FROM post_ratings WHERE timestamp_rated <= $SomeTimeStoredBetweenPages GROUP BY post_id) pr ON p.id = pr.post_id
WHERE p.post like '%test%'
ORDER BY pr.post_ratings DESC, p.unix_timestamp
DESC LIMIT ".(($PageNo - 1) * 20)." 20";
This is very much an example as I have no real idea of you table structures. Also not sure if you just have a row for each up vote, or whether there are down votes to take account of as well.