I would like to introduce myself as someone who has just recently started to fiddle a bit with SQL. Throughout my learning process I have come across a very specific problem and thus, my question is very specific too. Given the following table:
How should my list of commands look in order to get this following table:
In other words, what should I write to basically show the minimal salary and the id of its owner for each country. I have tried using GROUP BY but all I could get is the minimal salary per country whereas my goal was to show the id that belongs to the minimal salary too.
Hope I got my question clear and I thank everyone for the support.
This is a typical greatest-n-per-group problem.
One cross-database solution is to filter with a subquery:
select t.*
from mytable t
where t.salary = (select min(t1.salary) from mytable t1 where t1.country = t.country)
For performance with this query, you want an index on (country, salary).
You can also use window functions, if your database supports that:
select id, country, salary
from (
select t.*, rank() over(partition by country order by salary) rn
from mytable t
) t
where rn = 1
You can do by
select
id,
country,
salary
from
(
select
id,
country,
salary,
row_number() over (partition by country order by salary) as rnk
from table
)val
where rnk = 1
Related
I need help in writing an efficient query to find a list of toppers (students with maximum total marks in each class) when we are given individual scores for each subject across different classes. We are required to return 3 columns: class, topper_student name and topper_student_total marks.
I have used multiple sub-queries to find a solution. I am sure there would be much better implementations available for this problem (maybe via joins or window functions?).
Input table and my solution can be found at SQL Fiddle link.
http://www.sqlfiddle.com/#!15/2919e/1/0
Input table:
It would be clearer to use temporary tables to store results along the way and make the result traceable, but the solution can be achieved with a single query:
WITH student_marks AS (
SELECT Class_num, Name, SUM(Marks) AS student_total_marks
FROM School
GROUP BY Class_num, Name
)
SELECT Class_num, Name, student_total_marks
FROM (
SELECT Class_num, Name, student_total_marks, ROW_NUMBER() OVER(partition by Class_num order by student_total_marks desc, Class_num) AS beststudentfirst
FROM student_marks
) A
WHERE A.beststudentfirst = 1
The query within WITH statement calculate a sum of marks for every student in a class. At this point, subject is not required anymore. The result is temporarily stored into student_marks.
Next, we need to create a counter (beststudentfirst) using ROW_NUMBER to number the total marks from the highest to the lowest in each class (order by student_total_marks desc, Class_num). The counter should be reinitiated each time the class changes (partition by Class_num order).
From this last result, we only need the counter (beststudentfirst) with the value of one. It is the top student in each class.
Window functions are the most natural way to approach this. If you always want exactly three students, then use row_number():
select Class_num, Name, total_marks
from (select name, class_num, sum(marks) as total_marks,
row_number() over (partition by class_num order by sum(marks) desc) as seqnum
from School
group by Class_num, Name
) s
where seqnum <= 1
order by class_num, total_marks desc;
If you want to take ties into account, then use rank() or dense_rank().
Here is the SQL Fiddle.
select Class_num,[Name],total_marks from
(
select Row_number() over (partition by class_num order by Class_num,SUM(Marks) desc) as
[RN],Class_num,[Name],SUM(Marks) as total_marks
from School
group by Class_num,[Name]
)A
where RN=1
I am practicing SQL in Google Cloud Platform and have a table with the most popular names in USA.
I need to write a query that returns the most popular name in every year.
The Table has 6 columns: id, state, gender, year, name, Number of occurrences of the name
So far I have:
SELECT DISTINCT year
FROM 'table'
But I don't now what next...
What you are looking for is the called the mode in statistics. One way to get this uses aggregation and window fucntions:
select year, name
from (select year, name, count(*) as cnt,
row_number() over (partition by year order by count(*) desc) as seqnum
from t
group by year, name
) yn
where seqnum = 1;
The above version returns one arbitrary name if there are ties for the most frequent. If you do want ties, use rank() instead of row_number().
I am trying to work on public dataset bigquery-public-data.austin_crime.crime of the BigQuery. My goal is to get the output as three column that shows the
discription(of the crime), count of them, and top district for that particular description(crime).
I am able to get the first two columns with this query.
select
a.description,
count(*) as district_count
from `bigquery-public-data.austin_crime.crime` a
group by description order by district_count desc
and was hoping I can get that done with one query and then I tried this in order to get the third column showing me the Top district for that particular description (crime) by adding the code below
select
a.description,
count(*) as district_count,
(
select district from
( select
district, rank() over(order by COUNT(*) desc) as rank
FROM `bigquery-public-data.austin_crime.crime`
where description = a.description
group by district
) where rank = 1
) as top_District
from `bigquery-public-data.austin_crime.crime` a
group by description
order by district_count desc
The error i am getting is this. "Correlated subqueries that reference other tables are not supported unless they can be de-correlated, such as by transforming them into an efficient JOIN."
I think i can do that by joins. Can someone has better solution possibly to do that using without join.
Below is for BigQuery Standard SQL
#standardSQL
SELECT description,
ANY_VALUE(district_count) AS district_count,
STRING_AGG(district ORDER BY cnt DESC LIMIT 1) AS top_district
FROM (
SELECT description, district,
COUNT(1) OVER(PARTITION BY description) AS district_count,
COUNT(1) OVER(PARTITION BY description, district) AS cnt
FROM `bigquery-public-data.austin_crime.crime`
)
GROUP BY description
-- ORDER BY district_count DESC
I managed to get a query that works, but I'm curious if there is a more succinct way to construct it (still learning!).
The BigQuery dataset that I'm working with comes from Hubspot. It's being kept in sync by Stitch. (For those unfamiliar with BigQuery, most integrations are append-only so I have to filter out old copies via the ROW_NUMBER() OVER line you'll see below, so that's why it exists. Seems like the standard way to deal with this quirk.)
The wrinkle with the companies table is every single field, except for two ID ones, is of type RECORD. (See the screenshot at the bottom for an example). It serves to keep a history of field value changes. Unfortunately they don't seem to be in any order so wrapping up the fields - properties.first_conversion_event_name for example - in a MIN() or MAX() and grouping by companyid formula doesn't work.
This is what I ended up with (the final query is much longer; I didn't include all of the fields in the sample below):
WITH companies AS (
SELECT
o.companyid as companyid,
ARRAY_AGG(STRUCT(o.properties.name.value, o.properties.name.timestamp) ORDER BY o.properties.name.timestamp DESC)[SAFE_OFFSET(0)] as name,
ARRAY_AGG(STRUCT(o.properties.industry.value, o.properties.industry.timestamp) ORDER BY o.properties.industry.timestamp DESC)[SAFE_OFFSET(0)] as industry,
ARRAY_AGG(STRUCT(o.properties.lifecyclestage.value, o.properties.lifecyclestage.timestamp) ORDER BY o.properties.lifecyclestage.timestamp DESC)[SAFE_OFFSET(0)] as lifecyclestage
FROM (
SELECT *, ROW_NUMBER() OVER (PARTITION BY o.companyid ORDER BY o._sdc_batched_at DESC) as seqnum
FROM `project.hubspot.companies` o) o
WHERE seqnum = 1
GROUP BY companyid)
SELECT
companyid,
name.value as name,
industry.value as industry,
lifecyclestage.value as lifecyclestage
FROM companies
The WITH clause at the top is to get rid of the extra fields that the ARRAY_AGG(STRUCT()) includes. For each field I would have two columns - [field].value and [field].timestamp - and I only want the [field].value one.
Thanks in advance!
Schema Screenshot
I managed to get a query that works, but I'm curious if there is a more succinct way to construct it (still learning!).
Based on schema you presented and assuming your query really returns what you expect - below "optimized" version should return same result
#standardSQL
WITH companies AS (
SELECT
o.companyid AS companyid,
STRUCT(o.properties.name.value, o.properties.name.timestamp) AS name,
STRUCT(o.properties.industry.value, o.properties.industry.timestamp) AS industry,
STRUCT(o.properties.lifecyclestage.value, o.properties.lifecyclestage.timestamp) AS lifecyclestage
FROM (
SELECT *, ROW_NUMBER() OVER (PARTITION BY o.companyid ORDER BY o._sdc_batched_at DESC) AS seqnum
FROM `project.hubspot.companies` o
) o
WHERE seqnum = 1
)
SELECT
companyid,
name.value AS name,
industry.value AS industry,
lifecyclestage.value AS lifecyclestage
FROM companies
As you can see I just simply removed GROUP BY companyid because you already have just one entry/row per companyid after you apply WHERE seqnum = 1, so no reason at all to group just one row per companyid. For the very same reason I removed ARRAY_AGG( ORDER BY)[SAFE_OFFSET(0)] - it just aggregated one struct and then extracted that one element out of array - so no need in doing this
I need to get the Top 10 results for each Region, Market and Name along with those with highest counts (Gaps). There are 4 Regions with 1 to N Markets. I can get the Top 10 but cannot figure out how to do this without using a Union for every Market. Any ideas on how do this?
SELECT DISTINCT TOP 10
Region, Market, Name, Gaps
FROM
TableName
ORDER BY
Region, Market, Gaps DESC
One approach would be to use a CTE (Common Table Expression) if you're on SQL Server 2005 and newer (you aren't specific enough in that regard).
With this CTE, you can partition your data by some criteria - i.e. your Region, Market, Name - and have SQL Server number all your rows starting at 1 for each of those "partitions", ordered by some criteria.
So try something like this:
;WITH RegionsMarkets AS
(
SELECT
Region, Market, Name, Gaps,
RN = ROW_NUMBER() OVER(PARTITION BY Region, Market, Name ORDER BY Gaps DESC)
FROM
dbo.TableName
)
SELECT
Region, Market, Name, Gaps
FROM
RegionsMarkets
WHERE
RN <= 10
Here, I am selecting only the "first" entry for each "partition" (i.e. for each Region, Market, Name tuple) - ordered by Gaps in a descending fashion.
With this, you get the top 10 rows for each (Region, Market, Name) tuple - does that approach what you're looking for??
I think you want row_number():
select t.*
from (select t.*,
row_number() over (partition by region, market order by gaps desc) as seqnum
from tablename t
) t
where seqnum <= 10;
I am not sure if you want name in the partition by clause. If you have more than one name within a market, that may be what you are looking for. (Hint: Sample data and desired results can really help clarify a question.)