I am trying to run a dashboard with influxdb and grafana and i would like to show only the latest values of each id e.g. if i have a table something like this
id
utime
2
9:10AM
3
9:20AM
2
9:30AM
2
9:35AM
4
9:40AM
4
9:50AM
Now I would like to create a query in which it will only show me the latest result of each id and the result will show something like this below..
| 2 | 9:35AM |
| 3 | 9:20AM |
| 4 | 9:50AM |
I am new to this and don't know how exactly will it work. I have tried this query below but it didn't worked.
SELECT "id", "utime" FROM "http_listener_v2" WHERE $timeFilter GROUP BY "id"
Can somebody please help,how can I do this?
Related
SQL newbie here. I'm trying to write a query that generates a scoring table, setting null to a student's grades in a module for which they haven't yet taken their exams (on PostgreSQL).
So I start with tables that look something like this:
student_evaluation:
|student_id| module_id | course_id |grade |
|----------|-----------|-----------|-------|
| 1 | 1 | 1 |3 |
| 1 | 1 | 1 |7 |
| 1 | 2 | 1 |8 |
| 2 | 4 | 2 |9 |
course_module:
| module_id | course_id |
| ---------- | --------- |
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
In our use case, a course is made up of several modules. Each module has a single exam, but a student who failed his exam may have a couple of retries. The same module may also be present in different courses, but an exam attempt only counts for one instance of the module (ie. student A passed module 1's exam on course 1. If course 2 also has module 1, student A has to retake the same exam for course 2 if he also has access to that course).
So the output should look like this:
student_id
module_id
course_id
grade
1
1
1
3
1
1
1
7
1
2
1
8
1
3
1
null
2
4
2
9
I feel like this should have been a simple task, but I think I have a very flawed understanding of how outer and cross joins work. I have tried stuff like:
SELECT se.student_id, se.module_id, se.course_id, se.grade FROM student_evaluation se
RIGHT OUTER JOIN course_module ON course_module.course_id = se.course_id
AND course_module.module_id = se.module_id
or
SELECT se.student_id, se.module_id, se.course_id, se.grade FROM student_evaluation se
CROSS JOIN course_module WHERE course_module.course_id = se.course_id
Neither worked. These all feel wrong, but I'm lost as to what would be the proper way to go about this.
Thank you in advance.
I think you need both join types: first use a cross join to build a list of all combinations of students and courses, then use an outer join to add the grades.
SELECT sc.student_id,
sc.module_id,
sc.course_id,
se.grade
FROM student_evaluation se
RIGHT JOIN (SELECT s.student_id,
c.module_id,
c.course_id
FROM (SELECT DISTINCT student_id
FROM student_evaluation) AS s
CROSS JOIN course_module AS c) AS sc
USING (course_id));
How to increase value when source value is changed?
I have tried rank, dense_rank, row_number without success =(
id | src | how to get this?
--------
1 | 1 | 1
2 | 1 | 1
3 | 7 | 2
4 | 1 | 3
5 | 3 | 4
6 | 3 | 4
7 | 1 | 5
NOTICE: src is guaranteed to be in this order you see
is there simple way to do this?
You can achieve this by nesting two window functions - the first to get whether the src value changed from the previous row, the second to sum the number of changes. Unfortunately Postgres doesn't allow nesting window functions directly, but you can work around that with a subquery:
SELECT
id,
src,
sum(incr) OVER (ORDER BY id)
FROM (
SELECT
*,
(lag(src) OVER (ORDER BY id) IS DISTINCT FROM src)::int AS incr
FROM example
) AS _;
(online demo)
I've got a requirement to built a list report to show volume by 3 grouped by columns. The issue i'm having is if nothing happened on specific days for the specific grouped columns, i cant force it to show 0.
what i'm currently getting is something like:
ABC | AA | 01/11/2017 | 1
ABC | AA | 03/11/2017 | 2
ABC | AA | 05/11/2017 | 1
what i need is:
ABC | AA | 01/11/2017 | 1
ABC | AA | 02/11/2017 | 0
ABC | AA | 03/11/2017 | 2
ABC | AA | 04/11/2107 | 0
ABC | AA | 05/11/2017 | 1
ive tried going down the route of unioning a "dummy" query with no query filters, however there are days where nothing has happened, at all, for those first 2 columns so it doesn't always populate.
Hope that makes sense, any help would be greatly appreciated!
to anyone who wanted an answer i figured it out. Query 1 for just the dates, as there will always be some form of event happening daily so will always give a unique date range.
query 2 for the other 2 "grouped by" columns.
Create a data item in each with "1" as the result (but would work with anything as long as they are the same).
Query 1, left join to Query 2 on this new data item.
This then gives a full combination of all 3 columns needed. The resulting "Query 3" can then be left joined again to get the measures. Final query (depending on aggregation) may need to have the measure data item wrapped with a COALESCE/ISNULL to create a 0 on those days nothing happened.
Hi my table structure is like this i am using laravel and postgres database
id | serving_start_time | serving_end_time
1 | 2016-10-05 00:24:08.894 | 2016-10-05 00:24:19.003
2 | 2016-10-05 00:24:59.875 | 2016-10-05 00:25:13.728
3 | 2016-10-05 11:43:52.055 | 2016-10-05 11:45:41.561
I want to calculate the 'total_serving_time'(serving_start_time-serving_end_time) and get only the min and max 'total_serving_time'. Is this possible in one query? please help
In one query like following?
SELECT
MIN(serving_end_time - serving_start_time) AS min_total_serving_time,
MAX(serving_end_time - serving_start_time) AS max_total_serving_time
FROM table;
I use the last version of Talend 5.3.1.
I have a tmssqlInput which query my database like :
SELECT IdInvoice, DateInvoice, IdStuff, Name FROM Invoice
INNER JOIN Stuff ON Invoice.IdInvoice = Stuff.IdInvoice
which result in something like this
IdInvoice | DateInvoice | IdStuff | Name
1 | 2013-01-01 | 10 | test
1 | 2013-01-01 | 11 | test2
2 | 2013-02-01 | 12 | test3
2 | 2013-02-01 | 13 | test4
I'd like to export one file per invoice, here the specifications :
one header line with IdInvoice;DateInvoice
then one line per stuff like IdStuff;Name
example file 1:
1;2013-01-01
10;test
11;test2
example file 2 :
2;2013-02-01
12;test3
13;test4
how can I resolve that case with talend ?
Probably in tFileOutputDelimited but how can I have one file with multiple informations and iterate over each IdInvoice
Please go through the following link, you will get clear idea how to split data into multiple files
http://www.talendfreelancer.com/2013/09/talend-tflowtoiterate.html