It's possible to create a query that return the x/y number of records?
Eg.
I have table like this
ID | id_user | id_event
23 | 3 | 1
24 | 3 | 1
25 | 3 | 1
26 | 4 | 2
27 | 4 | 2
I will return something that looks like this:
Event
id_user 3 -> **1/3**
id_user 3 -> **2/3**
id_user 3 -> **3/3**
id_user 4 -> **1/2**
id_user 4 -> **2/2**
Any suggestion is appreciated!
Try this
SET #id_event := 0;
SELECT CONCAT('id_user ', id_user ,'->','**', (#id_event := #id_event + 1) ,'/', id_user ,** ) from table
This is probably a duplicate to this question.
SELECT CONCAT('id_user ',id_user,' -> **',rank,'/',group_total,'**') FROM (
SELECT id,
group_total,
CASE id_user
WHEN #id_user THEN
CASE id_event
WHEN #id_event THEN #rowno := #rowno + 1
ELSE #rowno := 1
END
ELSE #rowno :=1
END AS rank,
#id_user := id_user AS id_user,
#id_event := id_event AS id_event
FROM event_table
JOIN (SELECT id_user, id_event, COUNT(*) group_total FROM event_table GROUP BY id_user, id_event) t USING (id_user, id_event)
JOIN (SELECT #rowno := 0, #id_user := 0, #id_event := 0) r
ORDER BY id_user, id_event
) c;
Assuming you want output like this:
id_user < id_user > ** serial number of event related to this user / total events related to this user **
You can accomplish such result by the following query:
SELECT
CONCAT('id_user ',UE.id_user,' -> **',IF(#userID = UE.id_user, #eventNumber := #eventNumber + 1, #eventNumber := 1),'/',t.totalEvents,'**') AS output,
#userID := UE.id_user
FROM (SELECT #userID := -1, #eventNumber := 1) var,user_events UE
INNER JOIN
(
SELECT
id_user,
COUNT(id_event) totalEvents
FROM user_events
GROUP BY id_user
) AS t
ON UE.id_user = t.id_user
ORDER BY UE.id_user;
SQL FIDDLE DEMO
More:
SQL FIDDLE DEMO 2
This particular fiddle returns only the desired output column whereas the first fiddle contains one extra column
I played a little bit and that would be my solution:
SELECT id, id_user, id_event, if(#n = a.id_event, #c:=#c+1, if(#n:=a.id_event, #c:=1, #c:=1)) as count, (SELECT count(*) from TABLE b WHERE a.id_user = b.id_user) as total, from TABLE a join (SELECT #n:= "", #c:=1) c
It just have two if conditions for counting a #c up if #n and id_user matches if not #n become id_user and #c is 1 again. The join is for initialize the var in the same query.
Thx to that question, i found the answer to a questions that i asked 4 days ago.
Related
How would I go about creating group_ids in the following example based on the area(s) the users are active in?
group_id rep_id area datebegin dateend
1 1000 A 1/1/15 1/1/16
1 1000 B 1/1/15 1/1/16
2 1000 C 1/2/16 12/31/99
In the table you can see that rep 1000 was active in both A and B between 1/15 and 1/16. How would I go about coding the group_id field to group by datebegin & dateend?
Thanks for any help.
You can use variables in order to enumerate groups of records having identical rep_id, datebegin, dateend values:
SELECT rep_id, datebegin, dateend,
#rn := IF(#rep_id <> rep_id,
IF(#rep_id := rep_id, 1, 1),
#rn + 1) AS rn
FROM (
SELECT rep_id, datebegin, dateend
FROM mytable
GROUP BY rep_id, datebegin, dateend) AS t
CROSS JOIN (SELECT #rep_id := 0, #rn := 0) AS v
ORDER BY rep_id, datebegin
Output:
rep_id, datebegin, dateend, rn
-----------------------------------
1000, 2015-01-01, 2016-01-01, 1
1000, 2016-02-01, 2099-12-03, 2
You can use the above query as a derived table and join back to the original table. rn field is the group_id field you are looking for.
You can use variables to assign groups. As you said, only if the date_begin and date_end exactly match for 2 rows, they would be in the same group. Else a new group starts.
select rep_id,area,date_begin,date_end,
,case when #repid <> rep_id then #rn:=1 --reset the group to 1 when rep_id changes
when #repid=rep_id and #begin=date_begin and #end=date_end then #rn:=#rn --if rep_id,date_begin and date_end match use the same #rn previously assigned
else #rn:=#rn+1 --else increment #rn by 1
end as group_id
,#begin:=date_begin
,#end:=date_end
,#repid:=rep_id
from t
cross join (select #rn:=0,#begin:='',#end:='',#repid:=-1) r
order by rep_id,date_begin,date_end
The above query includes variables in the output. To only get the group_id use
select rep_id,area,date_begin,date_end,group_id
from (
select rep_id,area,date_begin,date_end
,case when #repid <> rep_id then #rn:=1
when #repid=rep_id and #begin=date_begin and #end=date_end then #rn:=#rn
else #rn:=#rn+1
end as group_id
,#begin:=date_begin
,#end:=date_end
,#repid:=rep_id
from t
cross join (select #rn:=0,#begin:='',#end:='',#repid:=-1) r
order by rep_id,date_begin,date_end
) x
I have a below table and wants to select only last 2 entries of all users.
Source table:
-------------------------------------
UserId | QuizId(AID)|quizendtime(AID)|
--------------------------------------
1 10 2016-5-12
2 10 2016-5-12
1 11 2016-6-12
2 12 2016-8-12
3 12 2016-8-12
2 13 2016-8-12
1 14 2016-9-12
3 14 2016-9-12
3 11 2016-6-12
Expected output is like, (should list only recent 2 quizid entries for all users)
-------------------------------------
UserId | QuizId(AID)|quizendtime(AID)|
--------------------------------------
1 14 2016-9-12
1 11 2016-6-12
2 13 2016-8-12
2 12 2016-8-12
3 14 2016-9-12
3 12 2016-8-12
Any idea's to produce this output.
Using MySQL user defined variables you can accomplish this:
SELECT
t.UserId,
t.`QuizId(AID)`,
t.`quizendtime(AID)`
FROM
(
SELECT
*,
IF(#sameUser = UserId, #a := #a + 1 , #a := 1) row_number,
#sameUser := UserId
FROM your_table
CROSS JOIN (SELECT #a := 1, #sameUser := 0) var
ORDER BY UserId , `quizendtime(AID)` DESC
) AS t
WHERE t.row_number <= 2
Working Demo
Note: If you want at most x number of entries for each user then change the condition in where clause like below:
WHERE t.row_number <= x
Explanation:
SELECT
*,
IF(#sameUser = UserId, #a := #a + 1 , #a := 1) row_number,
#sameUser := UserId
FROM your_table
CROSS JOIN (SELECT #a := 1, #sameUser := 0) var
ORDER BY UserId , `quizendtime(AID)` DESC;
This query sorts all the data in ascending order of userId and descending order of quizendtime(AID).
Now take a walk on this (multi) sorted data.
Every time you see a new userId assign a row_number (1). If you see the same user again then just increase the row_number.
Finally filtering only those records which are having row_number <= 2 ensures the at most two latest entries for each user.
EDIT: As Gordon pointed out that the evaluation of expressions using user defined variables in mysql is not guaranteed to follow the same order always so based on that the above query is slightly modified:
SELECT
t.UserId,
t.`QuizId(AID)`,
t.`quizendtime(AID)`
FROM
(
SELECT
*,
IF (
#sameUser = UserId,
#a := #a + 1,
IF(#sameUser := UserId, #a := 1, #a:= 1)
)AS row_number
FROM your_table
CROSS JOIN (SELECT #a := 1, #sameUser := 0) var
ORDER BY UserId , `quizendtime(AID)` DESC
) AS t
WHERE t.row_number <= 2;
WORKING DEMO V2
User-defined variables are the key to the solution. But, it is very important to have all the variable assignments in a single expression. MySQL does not guarantee the order of evaluation of expressions in a select -- and, in fact, sometimes processes them in different orders.
select t.*
from (select t.*,
(#rn := if(#u = UserId, #rn + 1,
if(#u := UserId, 1, 1)
)
) as rn
from t cross join
(select #u := -1, #rn := 0) params
order by UserId, quizendtime desc
) t
where rn <= 2;
Take a simple table such as:
User ID | Connection Date
1 | 12/10/2011
2 | 12/12/2011
1 | 12/14/2011
3 | 12/15/2011
1 | 12/16/2011
2 | 12/17/2011
2 | 12/18/2011
1 | 12/19/2011
3 | 12/20/2011
4 | 12/21/2011
2 | 12/21/2011
I would like to calculate the maximum date difference between a users connections.
Thanks
In days ...
select user_id, max(conn_date) - min(conn_date) from conn
group by user_id;
try as below
select
mainqry.userid,
max(mainqry.daysdiff) as max_date_diff
From
(
select
qry.userid,
-- qry.id1,
-- qry.currid,
( Case when qry.id1 = qry.currid then qry.dt1 else null end ) prevconndt,
qry.currdt,
datediff((Case when qry.id1 = qry.currid then qry.dt1 else null end),qry.currdt) daysdiff
from
(
select
userid,
#previd id1,
#previd := userid as currid,
#prevdt dt1,
#prevdt := connectiondate as currdt
from table1,(select #prevdt:=NULL,#previd := NULL) a
order by userid, connectiondate desc
) qry
) MainQry
group by MainQry.userid;
It will output below for your given data
Userid max_date_diff
1 4
2 5
3 5
4 Null
you can also verify it using below ...
select
qry.userid,
-- qry.id1,
-- qry.currid,
( Case when qry.id1 = qry.currid then qry.dt1 else null end ) prevconndt,
qry.currdt,
datediff((Case when qry.id1 = qry.currid then qry.dt1 else null end),qry.currdt) daysdiff
from
(
select
userid,
#previd id1,
#previd := userid as currid,
#prevdt dt1,
#prevdt := connectiondate as currdt
from table1,(select #prevdt:=NULL,#previd := NULL) a
order by userid, connectiondate desc
) qry
I have this Table , (sequence_No.) Field is null :
ID Name age sequence_No.
-- ----- --- ------------
1 sara 20
2 sara 20
3 sara 20
4 john 24
5 john 24
6 Hama 23
I want to Update it to this:
ID Name age sequence_No.
-- ----- --- ------------
1 sara 20 1
2 sara 20 2
3 sara 20 3
4 john 24 1
5 john 24 2
6 Hama 23 1
Which query can do that in mysql?
thank you
You can emulate ROW_NUMBER() using correlated subquery in mysql. The resulting table with sequential number will be join with the table itself and update the value of sequence_No using the generated numbers.
UPDATE tableName a
INNER JOIN
(
SELECT A.ID,
(
SELECT COUNT(*)
FROM tableName c
WHERE c.Name = a.Name AND
c.ID <= a.ID) AS sequence_No
FROM TableName a
) b ON a.ID = b.ID
SET a.sequence_No = b.sequence_No
SQLFiddle Demo
SELECT ID, Name, age, sequence_No
FROM
(
select ID,
Name,
age,
#sum := if(#nme = Name AND #acct = age, #sum ,0) + 1 sequence_No,
#nme := Name,
#acct := age
from TableName,
(select #nme := '', #sum := 0, #acct := '') vars
order by Name, age
) s
ORDER BY ID
Or you may use
SELECT
ID,
Name,
age,
(
CASE Name
WHEN #curType
THEN #curRow := #curRow + 1
ELSE #curRow := 1 AND #curType := Name END
) + 1 AS sequence_No
FROM student, (SELECT #curRow := 0, #curType := '') r
ORDER BY ID,NAME;
this would work though i have not tested yet you can use the same to update your table
Have a table photos
photos.id
photos.user_id
photos.order
A) Is it possible via a single query to group all photos by user and then update the order 1,2,3..N ?
B) added twist, what if some of the photos already have an order value associated? Make sure that the new photos.order never gets repeated and fills in ant orders lower or higher than those existing (as best as possible)
My only thought is just to run a script on this and loop through it and re'order' everything?
photos.id int(10)
photos.created_at datetime
photos.order int(10)
photos.user_id int(10)
Right now data may look like this
user_id = 1
photo_id = 1
order = NULL
user_id = 2
photo_id = 2
order = NULL
user_id = 1
photo_id = 3
order = NULL
the desired result would be
user_id = 1
photo_id = 1
order = 1
user_id = 2
photo_id = 2
order = 1
user_id = 1
photo_id = 3
order = 2
A)
You can use a variable that increments with each row and resets with each user_ID to get the row count.
SELECT ID,
User_ID,
`Order`
FROM ( SELECT #r:= IF(#u = User_ID, #r + 1,1) AS `Order`,
ID,
User_ID,
#u:= User_ID
FROM Photos,
(SELECT #r:= 1) AS r,
(SELECT #u:= 0) AS u
ORDER BY User_ID, ID
) AS Photos
Example on SQL Fiddle
B)
My First solution was to just add Order to the sorting that adds the row number, therefore anything with an Order Gets sorted by its order first, but this only works if your ordering system has no gaps and starts at 1:
SELECT ID,
User_ID,
RowNumber AS `Order`
FROM ( SELECT #r:= IF(#u = User_ID, #r + 1,1) AS `RowNumber`,
ID,
User_ID,
#u:= User_ID
FROM Photos,
(SELECT #i:= 1) AS r,
(SELECT #u:= 0) AS u
ORDER BY User_ID, `Order`, ID
) AS Photos
ORDER BY `User_ID`, `Order`
Example using Order Field
ORDERING WITH GAPS
I have eventually found a way of maintaining the sort order even when there are gaps in the sequence.
SELECT ID, User_ID, `Order`
FROM Photos
WHERE `Order` IS NOT NULL
UNION ALL
SELECT Photos.ID,
Photos.user_ID,
Numbers.RowNum
FROM ( SELECT ID,
User_ID,
#r1:= IF(#u1 = User_ID,#r1 + 1,1) AS RowNum,
#u1:= User_ID
FROM Photos,
(SELECT #r1:= 0) AS r,
(SELECT #u1:= 0) AS u
WHERE `Order` IS NULL
ORDER BY User_ID, ID
) AS Photos
INNER JOIN
( SELECT User_ID,
RowNum,
#r2:= IF(#u2 = User_ID,#r2 + 1,1) AS RowNum2,
#u2:= User_ID
FROM ( SELECT DISTINCT p.User_ID, o.RowNum
FROM Photos AS p,
( SELECT #i:= #i + 1 AS RowNum
FROM INFORMATION_SCHEMA.COLLATION_CHARACTER_SET_APPLICABILITY,
( SELECT #i:= 0) AS i
) AS o
WHERE RowNum <= (SELECT COUNT(*) FROM Photos P1 WHERE p.User_ID = p1.User_ID)
AND NOT EXISTS
( SELECT 1
FROM Photos p2
WHERE p.User_ID = p2.User_ID
AND o.RowNum = p2.`Order`
)
AND p.`Order` IS NULL
ORDER BY User_ID, RowNum
) AS p,
(SELECT #r2:= 0) AS r,
(SELECT #u2:= 0) AS u
ORDER BY user_ID, RowNum
) AS numbers
ON Photos.User_ID = numbers.User_ID
AND photos.RowNum = numbers.RowNum2
ORDER BY User_ID, `Order`
However as you can see this is pretty complicated. This works by treating those with an order value separately to those without. The top query just ranks all photos with no order value in order of ID for each user. The bottom query uses a cross join to generates a sequential list from 1 to n for each user ID (up to the number of entries for each User_ID). So with a data set like this:
ID User_ID Order
1 1 NULL
2 2 NULL
3 1 NULL
4 1 1
5 1 3
6 2 2
7 2 3
It would generate
UserID RowNum
1 1
1 2
1 3
1 4
2 1
2 2
2 3
It then uses NOT EXISTS to elimiate all combinations already used by Photos with a non null order, and ranked in order of RowNum partitioned by User_ID giving
UserID RowNum Rownum2
1 2 1
1 4 2
2 1 1
The RowNum2 value can then be matched with the rownum value achieved in the from subquery, giving the correct order value. Long winded, but it works.
Example on SQL Fiddle
Worked for me. I needed to increment version grouping by 4 fields (host, folder, fileName, status) and sort by 1 (downloadedAtTicks).
This is is my SELECT
SET #status := NULL;
SET #version := NULL;
SELECT
id,
host,
folder,
fileName,
status,
downloadedAtTicks,
version,
IF(IF(status IS NULL, 0, status) = #status, #version := #version + 1, #version := 0) AS varVersion,
#status := IF(status IS NULL, 0, status) AS varStatus
FROM csvsource
ORDER BY host, folder, fileName, status, downloadedAtTicks;
And this is my UPDATE
SET #status := NULL;
SET #version := NULL;
UPDATE
csvsource csv,
(SELECT
id,
IF(IF(status IS NULL, 0, status) = #status, #version := #version + 1, #version := 0) AS varVersion,
#status := IF(status IS NULL, 0, status) AS varStatus
FROM csvsource
ORDER BY host, folder, fileName, status, downloadedAtTicks) AS sub
SET
csv.version = sub.varVersion
WHERE csv.id = sub.id;