I'm relatively new to PostgreSQL and I'm working with window functions.
I have 2 relations: company and employee. Employee contains an information about the salary. I just wanna to get a rating of employees by their salary in ascending order.
This is my query.
SELECT company.name,
e.last_name,
e.salary,
rank() OVER (ORDER BY e.salary nulls first )
FROM company
LEFT JOIN employee e ON e.company_id = company.id
order by company.name;
So
result is:
You can see that fourth and eighth rows have null-value salary. But first row with not null salary value is sixth - Kulakov got the third rank, but I need him to have the second rank.
I think it's possible not to count not null values.
What is the right way to do this?
Related
table image
I have this table that I need to sort in the following way:
need to rank Departments by Salary;
need to show if Salary = NULL - 'No data to be shown' message
need to add total salary paid to the department
need to count people in the department
SELECT RANK() OVER (
ORDER BY Salary DESC
)
,CASE
WHEN Salary IS NULL
THEN 'NO DATA TO BE SHOWN'
ELSE Salary
,Count(Fname)
,Total(Salary) FROM dbo.Employees
I get an error saying:
Column 'dbo.Employees.Salary' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.
Why so?
Column 'dbo.Employees.Salary' is invalid in the select list because it
is not contained in either an aggregate function or the GROUP BY
clause.
Why so?
The aggregate functions are returning a single value for the whole table, you can't SELECT a field alongside them it doesn't makes sense. Like say, you have a students table you apply Sum(marks) for the whole students table, and you are then also selecting student's name Select studentname in your query. Which student's name will the database engine select? Confusing
Column "invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause"
I tried this-
using inner query
SELECT RANK() OVER (ORDER BY SAL DESC) RANK,FNAME,DEPARTMENT
CASE
WHEN SAL IS NULL THEN 'NO DATA TO BE SHOWN'
ELSE SAL
END
FROM
(SELECT COUNT(FNAME) FNAME, SUM(SALARY) SAL, DEPARTMENT
FROM TESTEMPLOYEE
GROUP BY DEPARTMENT) t
Suppose, I have following tables
product_prices
product|price|date
-------+-----+----------
apple |10 |2014-03-01
-------+-----+----------
apple |20 |2014-05-02
-------+-----+----------
egg |2 |2014-03-03
-------+-----+----------
egg |4 |2015-10-12
purchases:
user|product|date
----+-------+----------
John|apple |2014-03-02
----+-------+----------
John|apple |2014-06-03
----+-------+----------
John|egg |2014-08-13
----+-------+----------
John|egg |2016-08-13
What I need is table similar to this:
name|product|purchase date |price date|price
----+-------+--------------+----------+-----
John|apple |2014-03-02 |2014-03-01|10
----+-------+--------------+----------+-----
John|apple |2014-06-03 |2014-05-02|20
----+-------+--------------+----------+-----
John|egg |2014-08-13 |2014-08-13|2
----+-------+--------------+----------+-----
John|egg |2016-08-13 |2015-10-12|4
Or "what is the price for product at this day". Where price is calculated based on date from products table.
On real DB I tried to use something similar to:
SELECT name, product, pu.date, pp.date, pp.price
FROM purchases AS pu
LEFT JOIN product_prices AS pp
ON pu.date = (
SELECT date
FROM product_prices
ORDER BY date DESC LIMIT 1);
But I keep either getting only left part of table (with (null) instead of product dates and prices) or many rows with all the combinations of prices and dates.
I would suggest changing product_prices table to use a daterange column instead (or at least a start_date and an end_date).
You can use an exclusion constraint to make sure you never have overlapping ranges for one product and an insert trigger that "closes" the "current" prices and creates a new unbounded range for the newly inserted price.
A daterange can efficiently be indexed and with that in place the query gets as easy as:
SELECT name, product, pu.date, pp.valid_during, pp.price
FROM purchases AS pu
LEFT JOIN product_prices AS pp ON pu.date <# pp.valid_during
(assuming the range column is named valid_during)
The exclusion constraint would only work however if the product was an integer (not a varchar) - but I guess your real product_purchases table uses a foreign key to some product table anyway (which is an integer).
The new table definitions could look something like this:
create table purchase_prices
(
product_id integer not null references products,
price numeric(16,4) not null,
valid_during daterange not null
);
And the constraint that prevents overlapping ranges:
alter table purchase_prices
add constraint check_price_range
exclude using gist (product_id with =, valid_during with &&);
The constraint needs the btree_gist extension.
As always improving query speed comes with a price and in this case it's the higher maintenance costs for the GiST index. You would need to run some tests to see if the easier (and most probably much faster) query outweighs the slower insert performance on purchase_prices.
Look at your scalar sub-query very closely. It is not correlated back to the outer query. In other words, it will return the same result every time: the latest date in the product_prices table. Period. Think about the query out of context:
SELECT date
FROM product_prices
ORDER BY date DESC LIMIT 1
There are two problems with it:
It will return 2015-10-12 for every row in the join and ultimately, nothing was purchased on that date, hence, null.
Your approximation of closest is that the dates are equal. Unless you have a product_prices row for every product for every single date, you'll always have misses. "Closest" implies distance and ranking.
WITH close_prices_by_purchase AS (
SELECT
p.user,
p.product,
p.date pp.date,
pp.price,
row_number() over (partition by pp.product, order by pp.date desc) as distance -- calculate distance between purchase date and price date
FROM purchases AS p
INNER JOIN product_prices AS pp on pp.product = p.product
WHERE pp.date < p.date
)
SELECT user as name, product, pu.date as purchase_date, pp.date as price_date, price
FROM close_prices_by_purchase AS cpbp
WHERE distance = 1; -- shortest distance
You can try something like this, although I am sure there's a better way:
with diffs as (
select
a.*,
b."date" as bdate,
b.price,
b."date" - a."date" as diffdays,
row_number() over (
partition by "user", a."product", a."date"
order by "user", a."product", a."date", b."date" - a."date" desc
) as sr
from purchases a
inner join product_prices b on a.product = b.product
where b."date" - a."date" < 1
)
select
"user" as "name",
product,
"date" as "purchase date",
bdate as "price date",
price
from diffs
where sr = 1
Example: https://www.db-fiddle.com/f/dwQ9EXmp1SdpNpxyV1wc6M/0
Explanation
I attempted to join both tables and find the difference between dates of purchase and price, and ranked them by closest date prior to the purchase. Rank of 1 will go to the closest date. Then, data with rank of 1 was extracted.
This is a great place to use date ranges! We know the start date of the price range and we can use a window function to get the next date. At that point, it's really easy to figure out the price on any day.
with price_ranges as
(select product,
price,
date as price_date,
daterange(date, lead(date, 1)
OVER (partition by product order by date), '[)'
) as valid_price_range from product_prices
)
select "user" as name,
purchases.product,
purchases.date,
price_date,
price
from purchases
join price_ranges on purchases.product = price_ranges.product
and purchases.date <# price_ranges.valid_price_range
order by purchases.date;
i'm having problems with a query. I have two tables: country and city and i want to display the city with the highest population per country.
Here's the query:
select country.name as coname, city.name as ciname, max(city.population) as pop
from city
join country on city.countrycode=country.code
group by country.name
order by pop;`
Error
column "city.name" must appear in the GROUP BY clause or be used in an aggregate function.
I don't know how to solve this, i tried to make a subquery but it didn't work out.
How can i make it work?
You can easly get it using rank function:
select * from
(
select country.name as coname,
city.name as ciname,
city.population,
rank() over (partition by country.name order by city.population desc) as ranking
from
city
join
country
on city.countrycode=country.code
) A
where ranking = 1
The query below returns 9,817 records. Now, I want to SELECT one more field from another table. See the 2 lines that are commented out, where I've simply selected this additional field and added a JOIN statement to bind this new columns. With these lines added, the query now returns 649,200 records and I can't figure out why! I guess something is wrong with my WHERE criteria in conjunction with the JOIN statement. Please help, thanks.
SELECT DISTINCT dbo.IMPORT_DOCUMENTS.ITEMID, BEGDOC, BATCHID
--, dbo.CATEGORY_COLLECTION_CATEGORY_RESULTS.CATEGORY_ID
FROM IMPORT_DOCUMENTS
--JOIN dbo.CATEGORY_COLLECTION_CATEGORY_RESULTS ON
dbo.CATEGORY_COLLECTION_CATEGORY_RESULTS.ITEMID = dbo.IMPORT_DOCUMENTS.ITEMID
WHERE (BATCHID LIKE 'IC0%' OR BATCHID LIKE 'LP0%')
AND dbo.IMPORT_DOCUMENTS.ITEMID IN
(SELECT dbo.CATEGORY_COLLECTION_CATEGORY_RESULTS.ITEMID FROM
CATEGORY_COLLECTION_CATEGORY_RESULTS
WHERE SCORE >= .7 AND SCORE <= .75 AND CATEGORY_ID IN(
SELECT CATEGORY_ID FROM CATEGORY_COLLECTION_CATS WHERE COLLECTION_ID IN (11,16))
AND Sample_Id > 0)
AND dbo.IMPORT_DOCUMENTS.ITEMID NOT IN
(SELECT ASSIGNMENT_FOLDER_DOCUMENTS.Item_Id FROM ASSIGNMENT_FOLDER_DOCUMENTS)
One possible reason is because one of your tables contains data at lower level, lower than your join key. For example, there may be multiple records per item id. The same item id is repeated X number of times. I would fix the query like the below. Without data knowledge, Try running the below modified query.... If output is not what you're looking for, convert it into SELECT Within a Select...
Hope this helps....
Try this SQL: SELECT DISTINCT a.ITEMID, a.BEGDOC, a.BATCHID, b.CATEGORY_ID FROM IMPORT_DOCUMENTS a JOIN (SELECT DISTINCT ITEMID FROM CATEGORY_COLLECTION_CATEGORY_RESULTS WHERE SCORE >= .7 AND SCORE <= .75 AND CATEGORY_ID IN (SELECT DISTINCT CATEGORY_ID FROM CATEGORY_COLLECTION_CATS WHERE COLLECTION_ID IN (11,16)) AND Sample_Id > 0) B ON a.ITEMID =b.ITEMID WHERE a.(a.BATCHID LIKE 'IC0%' OR a.BATCHID LIKE 'LP0%') AND a.ITEMID NOT IN (SELECT DIDTINCT Item_Id FROM ASSIGNMENT_FOLDER_DOCUMENTS)
For Postgresql 8.x, I have an answers table containing (id, user_id, question_id, choice) where choice is a string value. I need a query that will return a set of records (all columns returned) for all unique choice values. What I'm looking for is a single representative record for each unique choice. I also want to have an aggregate votes column that is a count() of the number of records matching each unique choice accompanying each record. I want to force choice to lowercase for this comparison to be made (HeLLo and Hello should be considered equal). I can't GROUP BY lower(choice) because I want all columns in the result-set. Grouping by all columns causes all records to return, including all duplicates.
1. Closest I've gotten
select lower(choice), count(choice) as votes from answers where question_id = 21 group by lower(choice) order by votes desc;
The issue with this is it will not return all columns.
lower | votes
-----------------------------------------------+-------
dancing in the moonlight | 8
pumped up kicks | 7
party rock anthem | 6
sexy and i know it | 5
moves like jagger | 4
2. Trying with all columns
select *, count(choice) as votes from answers where question_id = 21 group by lower(choice) order by votes desc;
Because I am not specifying every column from the SELECT in my GROUP BY, this throws an error telling me to do so.
3. Specifying all columns in the GROUP BY
select *, count(choice) as votes from answers where question_id = 21 group by lower(choice), id, user_id, question_id, choice order by votes desc;
This simply dumps the table with votes column as 1 for all records.
How can I get the vote count and unique representative records from 1., but with all columns from the table returned?
Join grouped results back with primary table, then show only one row for each (question,answer) combination.
similar to this:
WITH top5 AS (
select question_id, lower(choice) as choice, count(*) as votes
from answers
where question_id = 21
group by question_id , lower(choice)
order by count(*) desc
limit 5
)
SELECT DISTINCT ON(question_id,choice) *
FROM top5
JOIN answers USING(question_id,lower(choice))
ORDER BY question_id, lower(choice), answers.id;
Here's what I ended up with:
SELECT answers.*, cc.votes as votes FROM answers join (
select max(id) as id, count(id) as votes
from answers
group by trim(lower(choice))
) cc
on answers.id = cc.id ORDER BY votes desc, lower(response) asc