I'm using a database to store results of an election with the columns id, candidate, post_time and result. Results are put in the database during 'counting the votes'. When a new update is available, a new entry will be inserted.
From this database, I would like to create a table with the most recent results (MAX post_time) per candidate (GROUP BY candidate), ordered by result (ORDER BY result).
How can I translate this to a working SQL-statement?
(I've tried mysql order and groupby without success)
I've tried:
SELECT *, MAX(time_post)
FROM [database]
GROUP BY candidate
HAVING MAX(time_post) = time_post
ORDER BY result
Assuming that you don't have multiple results per candidate at same time, next should work:
select r.candiate, r.result
from results r
inner join (
select candidate, max(post_time) as ptime
from results
group by candidate
) r2 on r2.candiate=r.candidate and r2.ptime=r.post_time
order by r.result
Note that MAX will not select the record with the maximum time, but it will select the maximum value from any record. So
SELECT MAX(a), MAX(b) FROM example
where exmple contains the two records a=1, b=2 and a=4, b=0, will result in a=4, b=2, which wasn't in the data. You should probably create a view with the latest votes only from each candidate, then query that. For performance, it may be sensible to use a materialized view.
Is the post_time likely to be the same for all the most recent results? Also does each candidate only appear once per post_time?
This could be achieved by just using a SELECT statement. Is there a reason you need the results in a new table?
If each candidate only appears once per post_time:
SELECT candidate, result
FROM table
WHERE post_time = (SELECT MAX(post_time) FROM table)
If you want to count how many times a candidate appears in the table for the last post_time:
SELECT candidate, count(result) as ResultCount
FROM table
WHERE post_time = (SELECT MAX(post_time) FROM table)
GROUP BY candidate
By what i see from ur attempts i'd think you should use this
SELECT MAX(post_time) FROM `table` GROUP BY candidate ORDER BY result
but the MAX statment only return a single value therefore i dont see why ORDER BY would be needed.
if you want multiple results try looking up the TOP statment
One way (tied results shown):
SELECT t.*
FROM tableX AS t
JOIN
( SELECT candidate
, MAX(time_post) AS time_post
FROM tableX
GROUP BY candidate
) AS m
ON (m.candidate, m.time_post) = (t.candidate, t.time_post)
ORDER BY t.result
and another one (no ties, only one row per candidate shown):
SELECT t.*
FROM
( SELECT DICTINCT candidate
FROM tableX
) AS d
JOIN
tableX AS t
ON t.PK = --- the Primary Key of the table, here
( SELECT ti.PK --- and here
FROM tableX AS ti
WHERE ti.candidate = d.candidate
ORDER ti.time_post DESC
LIMIT 1
)
ORDER BY t.result
Related
i need to create query with group by and order by, and i dont know how to do it.
query should return one record for the newest date for existing device_serial_number. enter image description here
so i would to get id 591 nad 592
solution can be in sql or the best way it will be in symfony, through query builder etc.
There are many ways to accomplish what you want.
First Way
The oldest way to select first, best, worst, whatever within a group is with a correlated subquery:
Select * from mytable outer
Where created_at = (
Select max(created_at)
from mytable inner
Where inner.device_serial_number = outer.device_serial_number
)
Second Way
Use a subselect to find earliest dates for all devices, them join back to the original table to filter:
Select a.*
From mytable a Inner Join
(Select device_serial_number, max(created_at) as latedate
From mytable b
Group By device_serial_number
) b
On a.device_serial_number=b.device_serial_number
And a.created_at=b.latedate
Third way
Use a window function to rank order all the dates and then pick the number one ranking.
Select * From (
Select *
, rank() Over (Partition By device_serial_number Order by created_at desc) as myrank
From mytable
)
Where myrank=1
Notice that while these 3 solutions use different aspects of SQL, they all have a common analytical approach. They are all two step processes whose first (inner) part involves finding the most recent created_at date for each device_serial_number and then reapplying that result back to the original table in the second (outer) part.
Here is
I want to show rows with same stop name one time..
How i use Query and While Loop
I see you have and id column. Assuming that it is unique you can do this all in sql query, no need for while loop.
You will need 2 queries; first will get the maximum (could be minimum also) available id of only one distinct stop name, the second is a join query with the first results and the main table. Something like this:
select * from tablename
inner join
(
select stop, max(id) as id from tablename
group by stop
)
as uniqueIDs
on tablename.id=uniqueIDs.id
u may try this..this will help you to fetch duplicates from table
SELECT tablename.stop FROM tablename INNER JOIN
(SELECT stop FROM tablename GROUP BY stop HAVING COUNT(id) > 1) dup
ON tablename.stop = dup.stop;
I have two tables:
twitterusers table
twittergrowth Table
I am trying to do JOIN these 2 tables, get all fields from twitteruser and selective fields from twittergrowth, then fetch only the last 3 rows from this data.
Expected Output:
Current Output:
I.e the rows are repeating. I want rows unique by ID or usernames, and the last set of timestamps. So it would be the last 3 rows, which has the most recent timestamps.
The code I could type scribble out is :
SELECT
t1.*,
t2.new_followers_count,
t2.new_friends_count,
t2.new_timestamp
FROM twitterusers t1
JOIN twittergrowth t2 on (t1.username=t2.username)
Searched quite few pages/sites, but cant really figure out how to do it. I would appreciate any help. :)
Additionally, I would like to get a LIMIT parameter added to the final result, so that I can paginate the full result.
First you need to find a maximum new_timestamp (latest) within groups of the same user_id and username in twittergrowth table. This is a classic group-wise maximum problem and the subquery tgmax does that. Then you need to join back the same table (tg this time) to get other columns that aren't in the group by clause of subquery and are not used in aggregate functions (like max()). These columns are new_followers_count and new_friends_count.
If you tried to put them in the select of subquery mysql would return values from an unspecified row from the same group and not necessarily the same as the one with the latest timestamp. This is explained here.
Once you get desired output for twittergrowth table the only thing left is to join twitterusers table to get all other columns.
SELECT tu.*, tg.new_followers_count, tg.new_friends_count, tg.new_timestamp
FROM twitterusers tu
JOIN twittergrowth tg
ON tu.user_id = tg.user_id AND tu.username = tg.username
JOIN
( SELECT tgg.user_id, tgg.username, max(tgg.new_timestamp) as latest_timestamp
FROM twittergrowth tgg
GROUP BY tgg.user_id, tgg.username ) tgmax
ON tg.user_id = tgmax.user_id AND tg.username = tgmax.username
AND tg.new_timestamp = tgmax.latest_timestamp
Note that this query would benefit from a composite index on (user_id,username,new_timestamp) in the twittergrowth table.
You need to group by to achieve your expected output.
GROUP BY id
To limit, or split results into pages, you can simply add LIMIT X,Y where X is the starting record and Y is the total number of records.
So a query to pull the expected results you want, but only the first 10 would be like so:
SELECT
t1.*,
t2.new_followers_count,
t2.new_friends_count,
t2.new_timestamp
FROM twitterusers t1
JOIN twittergrowth t2 on t1.username=t2.username
GROUP BY t1.id
LIMIT 0,10
This question already has answers here:
MySQL Order before Group by
(10 answers)
Closed 9 years ago.
I made a website for golf scorecards. The page I am working on is the players profile. When you access a players profile, it shows each course in order of last played (DESC). Except, the order of last played is jumbled due to the ORDER BY command below. Instead, when it GROUPs, it takes the earliest date, rather than the most recent.
After the grouping is done, it correctly shows them in order (DESC)... just the wrong order due to the courses grouping by date_of_game ASC, rather than DESC. Hope this isn't too confusing.. Thank you.
$query_patrol321 = "SELECT t1.*,t2.* FROM games t1 LEFT JOIN scorecards t2 ON t1.game_id=t2.game_id WHERE t2.player_id='$player_id' GROUP BY t1.course_id ORDER BY t1.date_of_game DESC";
$result_patrol321 = mysql_query($query_patrol321) or die ("<br /><br />There's an error in the MySQL-query: ".mysql_error());
while ($row_patrol321 = mysql_fetch_array($result_patrol321)) {
$player_id_rank = $row_patrol321["player_id"];
$course_id = $row_patrol321["course_id"];
$game_id = $row_patrol321["game_id"];
$top_score = $row_patrol321["total_score"];
Try to remove the GROUP BY-clause from the query. You should use GROUP BY only when you have both normal columns and aggregate functions (min, max, sum, avg, count) in your SELECT. You have just normal columns.
The fact that it shows the grouping result in ASC order is a coincidence because that is the order of their insertion. In contrast to other RDBMS like MS SQL Server, MySQL allows you to add non-aggregated columns to a GROUPed query. This non-standard behavior creates the confusion you're seeing. If this were not MySQL, you'd need to define the aggregation for all your selected columns given the grouping.
MySQL's behavior is (I believe) to take the first row matching the the GROUP for non-aggregated columns. I would advise against doing this.
Even though you're aggregating, you're not ORDERing by the aggregated column.
So What you want to do is ORDER BY the MAX date DESC
In this way, you are ordering by the latest date per course (your grouping criteria).
SELECT
t1.* -- It would be better if you actually listed the aggregations you wanted
,t2.* -- Which columns do you really want?
FROM
games t1
LEFT JOIN
scorecards t2
ON t2.[game_id] =t1[.game_id]
WHERE
t2.[player_id]='$player_id'
GROUP BY
t1.[course_id]
ORDER BY
MAX(t1.[date_of_game]) DESC
If you want the maximum date, then insert logic to get it. Don't depend on the ordering of columns or on undocumented MySQL features. MySQL explicitly discourages the use of non-aggregated columns in the group by when the values are not identical:
MySQL extends the use of GROUP BY so that the select list can refer to nonaggregated columns not named in the GROUP BY clause. This means that the preceding query is legal in MySQL. You can use this feature to get better performance by avoiding unnecessary column sorting and grouping. However, this is useful primarily when all values in each nonaggregated column not named in the GROUP BY are the same for each group. The server is free to choose any value from each group, so unless they are the same, the values chosen are indeterminate. (see [here][1])
How do you do what you want? The following query finds the most recent date on each course and just uses that -- and no group by:
SELECT t1.*, t2.*
FROM games t1 LEFT JOIN
scorecards t2
ON t1.game_id=t2.game_id
WHERE t2.player_id='$player_id' and
t1.date_of_game in (select MAX(date_of_game)
from games g join
scorecards ss
on g.game_id = ss.game_id and
ss.player_id = '$player_id'
where t1.course_id = g.course_id
)
GROUP BY t1.course_id
ORDER BY t1.date_of_game DESC
If game_id is auto incrementing, you can use that instead of date_of_game. This is particularly important if two games can be on the same course on the same date.
I need help with an advanced SQL-query (MSSQL 2000).
I have a table called Result that lists athletics 100 meter race-times. A runner can have several racetimes but I want to show only the best time from each runner.
The Result-table contains three columns, Result_id, athlete_id, result_time. So athlete_id must be unique when I list the values and result_time must be the fastest (lowest) value.
Any ideas?
In SQL Server 2000, you can't use windows functions. You can do this as follows:
select r.*
from result r join
(select athlete_id, min(result_time) as mintime
from result r
group by athlete_id
) rsum
on rsum.athlete_id = r.athlete_id and r.time = rsum.mintime
In more recent versions of SQL Server, you would use row_number().
If you simply need the fastest time for each athlete_id, do this:
select athelete_id, min(result_time) as FastestTime
from result
group by athelete_id
To show additional columns from the result table, you can join back to it like this:
select r.*
from result r
inner join (
select athelete_id, min(result_time) as FastestTime
from result
group by athelete_id
) rm on r.athelete_id = rm.athelete_id and r.result_time = rm.FastestTime
What you want is to use an aggregate function. in this case min() which will select the minumin data from all the rows that have the same data in the other selected columns. This means you also have to us the group by clause. The query below should give you the results you want.
Edit: If you need other columns, just bring them into the select clause, then add them to the group by clause like below:
select althlete_id, result_id, min(result_time) as result_time from result-table group by althlete_id, result_id
select althlete_id, result_id, min(result_time) as result_time, race_date from result-table group by althlete_id, race_date, result_id
Edit: You need to add all the columns into the group by that aren't part of an aggregate function. Aggregate functions are ones like min(), max(), avg() and so on.
Short answer: If you aren't putting a column in brackets, it probably has to be in the group by.