I am stuck with creating a column that would show aggregated numbers for number of created contacts.
I would like to achieve what it is visible in column C
SELECT x.date_period, count(x.vid) contacts FROM
(
SELECT c.firstname as owner, c.vid, to_char(c.properties__createdate__value::date, 'IYYYIW') as date_period
FROM "hmy"."contacts" as c
) x
group by x.date_period
Any ideas?
Thanks!
I believe you can just replace count(x.vid) with sum(x.vid) OVER(ORDER BY properties__createdate__value).
Here is a SQLFiddle exercising the idea. I built a table that replicates your example table. If you have the first two columns of the example built, you should be able to apply that line to it to create the running total.
Related
I am using postgres alongside sequelize. I have encountered a case where I need to write a coustom query which groups the records are a particular field. I know for the remaning columns that are not used for grouping, I need to use a aggregate function like SUM. But the problem is that for some columns I need to get the one what is the latest one (DESC sorted by created_at). I see no function in sql to do so. Is my only option to write subqueries or is there a better way? Thanks?
For better understanding, If you look at the below picture, I want the group the records with address. So after the query there should only be two records, one with sydney and the other with new york. But when it comes to the distance, I want the result of the query to contain the distance form the row that was most recently created, i.e with the latest created_at.
so the final two query results should be:
sydney 100 2022-09-05 18:14:53.492131+05:45
new york 40 2022-09-05 18:14:46.23328+05:45
select address, distance, created_at
from(
select address, distance, created_at, row_number() over(partition by address order by created_at DESC) as rn
from table) x
where rn = 1
So I have complicated query, to simplify let it be like
SELECT
t.*,
SUM(a.hours) AS spent_hours
FROM (
SELECT
person.id,
person.name,
person.age,
SUM(contacts.id) AS contact_count
FROM
person
JOIN contacts ON contacts.person_id = person.id
) AS t
JOIN activities AS a ON a.person_id = t.id
GROUP BY t.id
Such query works fine in MySQL, but Postgres needs to know that GROUP BY field is unique, and despite it actually is, in this case I need to GROUP BY all returned fields from returned t table.
I can do that, but I don't believe that will work efficiently with big data.
I can't JOIN with activities directly in first query, as person can have several contacts which will lead query counting hours of activity several time for every joined contact.
Is there a Postgres way to make this query work? Maybe force to treat Postgres t.id as unique or some other solution that will make same in Postgres way?
This query will not work on both database system, there is an aggregate function in the inner query but you are not grouping it(unless you use window functions). Of course there is a special case for MySQL, you can use it with disabling "sql_mode=only_full_group_by". So, MySQL allows this usage because of it' s database engine parameter, but you cannot do that in PostgreSQL.
I knew MySQL allowed indeterminate grouping, but I honestly never knew how it implemented it... it always seemed imprecise to me, conceptually.
So depending on what that means (I'm too lazy to look it up), you might need one of two possible solutions, or maybe a third.
If you intent is to see all rows (perform the aggregate function but not consolidate/group rows), then you want a windowing function, invoked by partition by. Here is a really dumbed down version in your query:
.
SELECT
t.*,
SUM (a.hours) over (partition by t.id) AS spent_hours
FROM t
JOIN activities AS a ON a.person_id = t.id
This means you want all records in table t, not one record per t.id. But each row will also contain a sum of the hours for all values that value of id.
For example the sum column would look like this:
Name Hours Sum Hours
----- ----- ---------
Smith 20 120
Jones 30 30
Smith 100 120
Whereas a group by would have had Smith once and could not have displayed the hours column in detail.
If you really did only want one row per t.id, then Postgres will require you to tell it how to determine which row. In the example above for Smith, do you want to see the 20 or the 100?
There is another possibility, but I think I'll let you reply first. My gut tells me option 1 is what you're after and you want the analytic function.
I have the first three columns in SQL. I want to create the 4th column called Count which counts the number of times each unique name appears in the Name column. I want my results to appears like the dataset below, so I don't want to do a COUNT and GROUP BY.
What is the best way to achieve this?
We can try to use COUNT window function
SELECT *,COUNT(*) OVER(PARTITION BY name ORDER BY year,month) count
FROM T
ORDER BY year,month
sqlfiddle
I have two tables with IDs and time stamps. Table 1 has two columns: ID and created_at. Table 2 has two columns: ID and post_date. I'd like to create a chart in Tableau that displays the Number of Records in Table 1 divided by Number of Records in Table 2, by week. How can I achieve this?
One way might be to use Custom SQL like this to create a new data source for your visualization:
SELECT created_table.created_date,
created_table.created_count,
posted_table.posted_count
FROM (SELECT TRUNC (created_at) AS created_date, COUNT (*) AS created_count
FROM Table1) created_table
LEFT JOIN
(SELECT TRUNC (post_date) AS posted_date, COUNT (*) AS posted_count
FROM Table2) posted_table
ON created_table.created_date = posted_table.posted_date
This would give you dates and counts from both tables for those dates, which you could group using Tableau's date functions in the visualization. I made created_table the first part of the left join on the assumption that some records would be created and not posted, but you wouldn't have posts without creations. If that isn't the case you will want a different join.
A question from a beginner.
I have two tables. One (A) contains Start_time, End_time, Status. Second one (B) contains Timestamp, Error_code. Second table is automatically logged by system every few seconds, so it contains lots of non unique values of Error_code (it changes randomly, but within a time range from table A). What i need is to select unique error code for every time range (in my case every row) from the first table for every time range in table A:
A.Start_time, A.End_time B.Error_code.
I have come to this:
select A.Start_time,
A.End_time,
B.Error_code
from B
inner join A
on B.Timestamp between A.Start_time and A.End_time
This is wrong, i know.
Any thoughts are welcome.
If tour query gives a lot of duplicates use distinct to remove them:
select DISTINCT A.Start_time, A.End_time, B.Error_code
from B
inner join A on B.Timestamp between A.Start_time and A.End_time