I have a table, like that one:
| B | 1 |
| C | 2 |
| B | 2 |
| A | 2 |
| C | 3 |
| A | 2 |
I would like to fetch it, but sorted and grouped. That is, I would like it grouped by the letter, but sorted by the highest sum of the group. Also, I want to show all entries within the group:
| C | 3 |
| C | 2 |
| A | 2 |
| A | 2 |
| B | 2 |
| B | 1 |
The order is that way because C has 3 and 2. 3+2=5, which is higher than 2+2=4 for A which in turn is higher than 2+1=3 for B.
I need to show all "grouped" letters because there are other columns that are distinct all of which I need shown.
EDIT:
Thanks for the quick reply. I have the audacity, however, to inquire further.
I have this query:
SELECT * FROM `ip_log` WHERE `IP` IN
(SELECT `IP` FROM `ip_log` GROUP BY `IP` HAVING COUNT(DISTINCT `uid`) > 1)
GROUP BY `uid` ORDER BY `IP`
The letters in the upper description are ip (I need it grouped by the IP addresses) and the numbers are timestamp (I need it sorted by the sum (or just used as the sorting parameter)). Should I create a temporary table and then use the solution below?
select t.Letter, t.Value
from MyTable t
inner join (
select Letter, sum(Value) as ValueSum
from MyTable
group by Letter
) ts on t.Letter = ts.Letter
order by ts.ValueSum desc, t.Letter, t.Value desc
SQL Fiddle Example
If your table's columns are letter and number, the way I would go around to doing this would be the following:
SELECT
letter,
GROUP_CONCAT(number ORDER BY number DESC),
SUM(number) AS total
FROM table
GROUP BY letter
ORDER BY total desc
What you will get, based on your example is the following:
| C | 3,2 | 5
| A | 2,2 | 4
| B | 2,1 | 3
You can then process that data to get the actual information you want/need.
If you still want the data in the format you requested originally, it is not possible with a single query. The reason for that is that you can't sort based on an aggregated data that you are not calculating in the same query (the SUM of the number column). So you will need to make a sub-query to calculate that and feed it back into the original query (disclaimer: untested query):
SELECT
letter,
number
FROM table
JOIN (SELECT ltr, SUM(number) AS total FROM table GROUP BY letter) AS totals
ON table.letter = totals.ltr
ORDER BY totals.total desc, letter desc, number desc
Related
I have 5 different datasets from 5 different tables.. From those 5 different tables I have taken below group by data..
select number,count(*) as total from tb01 group by number limit 5;
select number,count(*) as total from tb02 group by number limit 5;
Like that I can retrieve 5 different datasets. Here is an example.
+-----------+-------+
| number | total |
+-----------+-------+
| 114000259 | 1 |
| 114000400 | 1 |
| 114000686 | 1 |
| 114000858 | 1 |
| 114003895 | 1 |
+-----------+-------+
Now I need to combine those 5 different tables such as below tabular format.
+-----------+-------+-------+-------+
| number | tb01 | tb02 | tb03 |
+-----------+-------+-------+-------+
| 114000259 | 1 | 2 | 1 |
| 114000400 | 1 | 0 | 1 |
| 114000686 | 1 | 3 | 1 |
| 114000858 | 1 | 1 | 5 |
| 114003895 | 1 | 0 | 1 |
+-----------+-------+-------+-------+
Can someone help me to combine those 5 grouped data sets and get the union as above.
Note: I dont need the header as same as table names..these headers can be anything
Further I dont need to limit 5, above is to get a sample of 5 data only. I have a large dataset.
It's a job for JOINs and subqueries. My answer will consider three tables. It should be obvious how to expand it to five.
Your first subquery: get all possible numbers.
SELECT number FROM tb01 UNION
SELECT number FROM tb02 UNION
SELECT number FROM tb03
Then you have a subquery for each table to get the count.
SELECT number, COUNT(*) AS total
FROM tb02 GROUP BY number
Then you LEFT JOIN everything and SELECT from that.
SELECT numbers.number,
tb01.total tb01,
tb02.total tb02,
tb03.total tb03
FROM (
SELECT number FROM tb01 UNION
SELECT number FROM tb02 UNION
SELECT number FROM tb03
) numbers
LEFT JOIN (
SELECT number, COUNT(*) AS total
FROM tb01 GROUP BY number
) tb01 ON numbers.number = tb01.number
LEFT JOIN (
SELECT number, COUNT(*) AS total
FROM tb02 GROUP BY number
) tb02 ON numbers.number = tb02.number
LEFT JOIN (
SELECT number, COUNT(*) AS total
FROM tb03 GROUP BY number
) tb03 ON numbers.number = tb01.number
You can add ORDER BY and LIMIT clauses to that overall query as necessary.
The first subquery together with the LEFT JOIN ensures that you get results even if some of your tables are missing number rows. (Some DBMSs have FULL OUTER JOIN, but MySQL does not.)
Pro tip: If you use LIMIT without ORDER BY, you get an unpredictable subset of your rows. Unpredictable is worse than random, because you get the same subset in testing with small tables, but when your tables grow you may start getting different subsets. You'll never catch the problem in unit testing. LIMIT without ORDER BY is a serious error.
I want to show first two top voted Posts then others sorted by id
This is table
+----+-------+--------------+--------+
| Id | Name | Post | Votes |
+====+=======+==============+========+
| 1 | John | John's msg | -6 |
| 2 |Joseph |Joseph's msg | 8 |
| 3 | Ivan | Ivan's msg | 3 |
| 4 |Natalie|Natalie's msg | 10 |
+----+-------+--------------+--------+
After query result should be:
+----+-------+--------------+--------+
| Id | Name | Post | Votes |
+====+=======+==============+========+
| 4 |Natalie|Natalie's msg | 10 |
| 2 |Joseph |Joseph's msg | 8 |
-----------------------------------------------
| 1 | John | John's msg | -6 |
| 3 | Ivan | Ivan's msg | 3 |
+----+-------+--------------+--------+
I have 1 solution but i feel like there is better and faster way to do it.
I run 2 queries, one to get top 2, then second to get others:
SELECT * FROM table order by Votes desc LIMIT 2
SELECT * FROM table order by Id desc
And then in PHP i make sure that i show 1st query as it is, and on displaying 2nd query i remove entry's that are in 1st query so they don't double.
Can this be done in single query to select first two top voted, then others?
You would have to use subqueries or union - meaning you have a single outer query, which contains multiple queries inside. I would simply retrieve the IDs from the first query and add a id not in (...) criterion to the where clause of the 2nd query - thus filtering out the posts retrieved in the first query:
SELECT * FROM table WHERE Id NOT IN (...) ORDER BY Id DESC
With union the query would look like as follows:
(SELECT table.*, 1 as o FROM table order by Votes desc LIMIT 2)
UNION
(SELECT table.*, 0 FROM table
WHERE Id NOT IN (SELECT Id FROM table order by Votes desc LIMIT 2))
ORDER BY o DESC, if(o=1,Votes,Id) DESC
As you can see, it wraps 3 queries into one and has a more complicated ordering as well because in union the order of the records retrieved is not guaranteed.
Two simple queries seem to be a lot more efficient to me in this particular case.
There could be different ways to write a query that returns the rows in the order you want. My solution is this:
select
table.*
from
table left join (select id from table order by votes desc limit 2) l
on table.id = l.id
order by
case when l.id is not null then votes end desc,
tp.id
the subquery will return the first two id ordered by votes desc, the join will succeed whenever the row is one of the first two otherwise l.id will be null instead.
The order by will order by number of votes desc whenever the row is the first or the second (=l.id is not null), when l.id is null it will put the rows at the bottom and order by id instead.
Student table :
----------------------
id | name
______________________
1 | Name 1
2 | Name 2
Course Table :
id | student_id | ctype | level
__________________________________
1 | 2 | beginner | complete
2 | 2 | advanced | current
3 | 1 | beginner | current
4 | 2 | intermed | skipped
From the above two table i am trying to get the latest user records based on the level from course table . the level should be matched such that it checks for current, complete and skipped in the same order so if the user has a level of current for any course type it should be fetched else check the level complete...
i am using the following query .
SELECT `sc`.`student_id`,
`s`.`name`,
`sc`.`id` as `course_id`,
`sc`.`ctype`,
`sc`.`level`,
FROM `course` `sc`
LEFT JOIN `students` `s` ON `s`.`id` = `sc`.`student_id`
WHERE sc.id = (SELECT ssc.id FROM course ssc WHERE ssc.student_id = sc.student_id
ORDER BY FIELD(`ssc`.`level`,"current","complete","skipped") DESC LIMIT 1,1)
GROUP BY `sc`.`student_id`
ORDER BY `sc`.`id` DESC
LIMIT 20
The problem with the above query is it displays only if there is more than one user id matching in course table . so the final output i get is it displays only the student with id 2 and ignore the student with id 1 as there is no more than one .
Result form above query
student_id | name | course_id | ctype | level |
=====================================================
2 | Name 2 | 2 | advanced | current
Expected Result
student_id | name | course_id | ctype | level |
=====================================================
2 | Name 2 | 2 | advanced | current
1 | Name 1 | 3 | beginner | current
NOTE : I have also tried FIELD_IN_SET and IN instead of FIELD im getting the same result
Change LIMIT 1,1 to LIMIT 0,1 or just LIMIT 1.
Unlike most other things in SQL, the offset field in the LIMIT clause is 0-based, not 1-based. So if there's only 1 matching row, LIMIT 1,1 skips over it. And if there are 2 or more matching rows, you're not getting the top match, you're getting the 2nd match.
Also, the ordering should be ASC, not DESC, since you want to prefer the lowest field (current), not the highest.
SELECT `sc`.`student_id`,
`s`.`name`,
`sc`.`id` as `course_id`,
`sc`.`ctype`,
`sc`.`level`
FROM `course` `sc`
LEFT JOIN `students` `s` ON `s`.`id` = `sc`.`student_id`
WHERE sc.id = (
SELECT ssc.id FROM course ssc
WHERE ssc.student_id = sc.student_id
ORDER BY FIELD(`ssc`.`level`,"current","complete","skipped") ASC
LIMIT 0,1)
GROUP BY `sc`.`student_id`
ORDER BY `sc`.`id` DESC
LIMIT 20
DEMO
There's also no need for GROUP BYsc.student_id`. The query is only returning one course ID per student, so there can't be multiple rows for each student.
I have a table like this:
Table: p
+----------------+
| id | w_id |
+---------+------+
| 5 | 8 |
| 5 | 10 |
| 5 | 8 |
| 5 | 10 |
| 5 | 8 |
| 6 | 5 |
| 6 | 8 |
| 6 | 10 |
| 6 | 10 |
| 7 | 8 |
| 7 | 10 |
+----------------+
What is the best SQL to get the following result? :
+-----------------------------+
| id | most_used_w_id |
+---------+-------------------+
| 5 | 8 |
| 6 | 10 |
| 7 | 8 |
+-----------------------------+
In other words, to get, per id, the most frequent related w_id.
Note that on the example above, id 7 is related to 8 once and to 10 once.
So, either (7, 8) or (7, 10) will do as result. If it is not possible to
pick up one, then both (7, 8) and (7, 10) on result set will be ok.
I have come up with something like:
select counters2.p_id as id, counters2.w_id as most_used_w_id
from (
select p.id as p_id,
w_id,
count(w_id) as count_of_w_ids
from p
group by id, w_id
) as counters2
join (
select p_id, max(count_of_w_ids) as max_counter_for_w_ids
from (
select p.id as p_id,
w_id,
count(w_id) as count_of_w_ids
from p
group by id, w_id
) as counters
group by p_id
) as p_max
on p_max.p_id = counters2.p_id
and p_max.max_counter_for_w_ids = counters2.count_of_w_ids
;
but I am not sure at all whether this is the best way to do it. And I had to repeat the same sub-query two times.
Any better solution?
Try to use User defined variables
select id,w_id
FROM
( select T.*,
if(#id<>id,1,0) as row,
#id:=id FROM
(
select id,W_id, Count(*) as cnt FROM p Group by ID,W_id
) as T,(SELECT #id:=0) as T1
ORDER BY id,cnt DESC
) as T2
WHERE Row=1
SQLFiddle demo
Formal SQL
In fact - your solution is correct in terms of normal SQL. Why? Because you have to stick with joining values from original data to grouped data. Thus, your query can not be simplified. MySQL allows to mix non-group columns and group function, but that's totally unreliable, so I will not recommend you to rely on that effect.
MySQL
Since you're using MySQL, you can use variables. I'm not a big fan of them, but for your case they may be used to simplify things:
SELECT
c.*,
IF(#id!=id, #i:=1, #i:=#i+1) AS num,
#id:=id AS gid
FROM
(SELECT id, w_id, COUNT(w_id) AS w_count
FROM t
GROUP BY id, w_id
ORDER BY id DESC, w_count DESC) AS c
CROSS JOIN (SELECT #i:=-1, #id:=-1) AS init
HAVING
num=1;
So for your data result will look like:
+------+------+---------+------+------+
| id | w_id | w_count | num | gid |
+------+------+---------+------+------+
| 7 | 8 | 1 | 1 | 7 |
| 6 | 10 | 2 | 1 | 6 |
| 5 | 8 | 3 | 1 | 5 |
+------+------+---------+------+------+
Thus, you've found your id and corresponding w_id. The idea is - to count rows and enumerate them, paying attention to the fact, that we're ordering them in subquery. So we need only first row (because it will represent data with highest count).
This may be replaced with single GROUP BY id - but, again, server is free to choose any row in that case (it will work because it will take first row, but documentation says nothing about that for common case).
One little nice thing about this is - you can select, for example, 2-nd by frequency or 3-rd, it's very flexible.
Performance
To increase performance, you can create index on (id, w_id) - obviously, it will be used for ordering and grouping records. But variables and HAVING, however, will produce line-by-line scan for set, derived by internal GROUP BY. It isn't such bad as it was with full scan of original data, but still it isn't good thing about doing this with variables. On the other hand, doing that with JOIN & subquery like in your query won't be much different, because of creating temporery table for subquery result set too.
But to be certain, you'll have to test. And keep in mind - you already have valid solution, which, by the way, isn't bound to DBMS-specific stuff and is good in terms of common SQL.
Try this query
select p_id, ccc , w_id from
(
select p.id as p_id,
w_id, count(w_id) ccc
from p
group by id,w_id order by id,ccc desc) xxx
group by p_id having max(ccc)
here is the sqlfidddle link
You can also use this code if you do not want to rely on the first record of non-grouping columns
select p_id, ccc , w_id from
(
select p.id as p_id,
w_id, count(w_id) ccc
from p
group by id,w_id order by id,ccc desc) xxx
group by p_id having ccc=max(ccc);
I've got a table with the most common colors in images. It looks something like this:
file | color | count
---------------------
1 | ffefad | 166
1 | 443834 | 84
2 | 74758a | 3874
2 | abcdef | 228
2 | 876543 | 498
3 | 543432 | 3382
3 | abcdef | 483
I'm trying to get the most common color for each image. So I'd like my result to be:
file | color | count
---------------------
1 | ffefad | 166
2 | 74758a | 3874
3 | 543432 | 3382
So my problem seems to be that I need to GROUP BY the file column, but MAX() the count column. But simply
SELECT h.file, h.color, MAX(h.count) FROM histogram GROUP BY h.file
isn't working because it's indeterminate, so the color result won't match the row from the count result.
SELECT h.file, h.color, MAX(h.count) FROM histogram GROUP BY h.file, h.color
fixes the determinacy, but now every row is "unique" and all rows are returned.
I can't figure out a way to do a subquery or join, since the only "correct" values I can figure to get, file and count, are not distinct by themselves.
Perhaps I need a saner schema? It's "my" table so I can change that if need be.
SELECT tbl.file, tbl.color, tbl.count
FROM tbl
LEFT JOIN tbl as lesser
ON lesser.file = tbl.file
AND tbl.count < lesser.count
WHERE lesser.file IS NULL
order by tbl.file
select file , max(count)
FROM histogram
GROUP BY h.file
This will give the max(count) by file. Turn it into a subquery and inner join so it acts as a filter.
select h.file, h.colour, h.count
from histogram inner join
(select file , max(count) as maxcount
FROM histogram
GROUP BY h.file) a
on a.file = h.file and a.maxcount = h.count
This will respond with 2 rows if there are more than 1 colour with the same max count.