My Question is:
Germany (population 80 million) has the largest population of the
countries in Europe. Austria (population 8.5 million) has 11% of the
population of Germany.
Show the name and the population of each country in Europe. Show the
population as a percentage of the population of Germany.
My answer:
SELECT name,CONCAT(ROUND(population/80000000,-2),'%')
FROM world
WHERE population = (SELECT population
FROM world
WHERE continent='Europe')
What I am doing wrong?
Thanks.
The question was incomplete and was taken from here
This is the answer
SELECT
name,
CONCAT(ROUND((population*100)/(SELECT population
FROM world WHERE name='Germany'), 0), '%')
FROM world
WHERE population IN (SELECT population
FROM world
WHERE continent='Europe')
I was wondering about sub-query as from OP'S question it wasn't clear (at least to me). The reason is that "world" table (as the name suggest, I have to admit) contains all world country whereas we're interested only into european one. Moreover, the population of Germany has to be retrieved from DB because it's not extacly 80.000.000; if you use that number you receive back 101% as Germany population.
When using sql server in SQL Zoo, then don't use CONCAT:
I think SQL Zoo uses a version of SQL Server that doesn't support CONCAT and furthermore it looks like you have to do a CAST. Instead concatenate with the use of '+'. Also see this post.
I figure the script should be something like beneath (though I haven't got it to my desired stated, because of the fact I want to result to look like 3%;0%;4%;etc. instead of 3.000000000000000%;0.000000000000000%;4.000000000000000%;etc.. And I start a new topic for that one here).
SELECT
name,
CAST(ROUND(population*100/(SELECT population FROM world WHERE name='Germany'), 0) as varchar(20)) +'%'
FROM world
WHERE population IN (SELECT population
FROM world
WHERE continent='Europe')
select name, CONCAT(ROUND((population/(select population from world where name = "Germany"))*100),"%")
from world
where continent= "Europe"
SELECT name, CONCAT(ROUND(population/(SELECT population FROM world WHERE name = 'Germany')*100,0), '%')
FROM world
WHERE continent = 'Europe'
As of this writing (Aug 16th, 2022), the accepted answer is a percentage without trailing 0s.
Using CONCAT and CAST solves this.
SELECT name, CONCAT(CAST(100*ROUND((population / (SELECT population FROM world WHERE name ='Germany')), 2) AS INT), '%')
FROM world
WHERE continent = 'Europe';
sub query should be return multiple data so you can use in function like this
SELECT name,CONCAT(ROUND(population/80000000,-2),'%')
FROM world
WHERE population IN (SELECT population
FROM world
WHERE continent='Europe')
Below added code snippet
select name, concat (round(population/(select population from world where
name='germany')*100,0), '%') from world where continent='Europe'
The following worked for me:
SELECT name, concat(format(ROUND(population / (SELECT population FROM world WHERE name = 'Germany') * 100, 5), '0'), '%') AS percentage
FROM world
WHERE continent = 'Europe';
Related
I would appreciate a little help on some script in sql. So I have a list like the one below and a database table -Table1 with statement as a colum name, and I will like to create a column called location, where the script can search in the statement column and once it finds any of the items in the list in any row it states that in the location column
(Tema, london, Sydney, Germany, China, Africa,)
Statement
-------------------
Going to london
Apples in Tema
Sydney is a city
China is a country
Africa is a continent
In the end I hope to see a table like this :
Statement
location
Going to london
London
Apples in Tema
Tema
Sydney is a city
Sydney
china is a country
China
Africa is a continent
Africa
By using this script,
SELECT Statement,
Case
WHEN Statement::text ~~* '%london%'::character varying::text
THEN 'london'::character varying
ELSE NULL::character varying
END AS location
FROM Table1
I think I would have to write a very tall script, but I was wondering if I could get help with something efficient and quite simple to achieve this
If you have a list of places, you can use that:
select t1.*, v.place
from table1 t1 cross join
(values ('tema'), ('london'), ('sydney'), ('germany'), ('china'), ('africa')
) v(place)
on Statement::text ilike '%' || v.place || '%';
Note: You might want to use regular expressions so you can include work boundaries but your example code doesn't do tis.
We are learning SQL at school, and my professor has this sql code in his documents.
SELECT wp.city, (COUNT(*) / locations.area) AS population_density
FROM world_poulation AS wp
INNER JOIN location
ON wp.city = locations.city
WHERE locations.state = “Hessen”
GROUP BY wp.city, locations.area
Everything is almost clear for me, just the aggregate function with /locations.area doesn't make any sense to me. Can anybody help?
Thank you in advance!
Look at what the query is grouped on, that tells you what each group consists of. In this case, each group is a city, and contains all the rows that have the same value for wp.city (and as the location table is joined on that value too, the locations.area is only included in the grouping so that it can be used in the result).
So each group has a number of rows, and the COUNT(*) aggregate will contain the number of rows for each group. The value of (COUNT(*) / locations.area) will be the number of rows in the group divided by the value of locations.area for that group.
If you would have data like this:
world_population
name city
--------- ---------
John London
Peter London
Sarah London
Malcolm London
Ian Cardiff
Johanna Stockholm
Sven Stockholm
Egil Stockholm
locations
city state area
----------- -------------- ---------
London Hessen 2
Cardiff Somehere else 14
Stockholm Hessen 1
Then you would get a result with two groups (as Cardiff is not in the state Hessen). One group has four people from London which has the area 2, so the population density would be 2. The other group has three people from Stockholm which has the area 1, so the population density would be 3.
Side note: There is a typo in the query, as it joins in the table location but refers to it as locations everywhere else.
Try writing it like:
SELECT wp.city,
locations.area,
COUNT(*) AS population,
(COUNT(*) / locations.area) AS population_density
FROM world_poulation AS wp
INNER JOIN location
ON wp.city = locations.city
WHERE locations.state = “Hessen”
GROUP BY wp.city, locations.area
The key is the GROUP BY statement. You are showing pairs of cities and areas. The COUNT(*) is the number of times a given pair shows up in the table you created by joining world population and location. The area is just a number, so you can divide the area by the COUNT.
Having some trouble understanding this query, particularly the WHERE in the subquery. I don't really get what it is accomplishing. Any help would be appreciated. Thanks
# Find the largest country (by area) in each continent. Show the continent,
# name, and area.
SELECT continent, name, area
FROM countries AS a
WHERE area = (
SELECT MAX(area)
FROM countries AS b
WHERE a.continent = b.continent
)
Consider the following subset of the countries data:
Continent Country Area
North America USA 3718691
North America Canada 3855081
North America Mexico 761602
Europe France 211208
Europe Germany 137846
Europe UK 94525
Europe Italy 116305
This is a correlated query that behaves as follows:
Reads the first row returned by the outer query (North America, USA, 3718691)
Runs the subquery which correlates to a.continent, North America, and returns 3855081 which is the maximum area in North America.
Does the where equality which checks to see if 3855081 matches the area on the row we're working on.
It doesn't match so the next row in the outer query is read and we start over at step 1 this time working on the second row.
Repeat for all rows in the outer query.
When we're looking at rows 2 and 4, step 4. will match so those rows will be returned by the query.
You can check the results by using this data in your countries table and running the query.
Note that this is a very poor way to determine the country with the maximum area per continent because it repeats the subquery for every country. Using my sample data, it determines the maximum area for North America 3 times and the maximum area for Europe 4 times.
Since you asked in your comment, I would write this query as follows:
SELECT a.continent, a.name, a.area
FROM countries AS a
inner join (select continent, max(area) max_area
from countries
group by continent) as b on a.continent = b.continent
WHERE a.area = b.max_area
In this version of the query, the maximum for each continent is only determined once. The original query was written to illustrate correlated queries and it's important to understand them. Correlated queries can often be used to resolve complex logic.
The subquery is finding the maximum area for countries. Which countries? All countries that match the continent of the country in the outer query.
So, for each country it gets the area of the largest country on the same continent.
The WHERE clause then says "are the two areas the same -- the maximum area and the area of this country?". It chooses only countries that have the maximum area.
I have 2 tables- Economics (land_code, gdp) and Continent (Land_code, Cont, Percentage). I need to create a query that calculates average GDP for Continent. In case the country is at the same time in several continents, we should also consider the percentage of GDP that belongs to continent. As I have understood if Egypt has GDP of 100, then 90 belongs to Africa and 10 to Asia, how can I implement this expression?
!!! ALREADY DONE)
Obviously,
select Economics.land_code, Economics.gdp * Continent.Percentage
from ...
This is a heavily simplified version of an SQL problem I'm dealing with. Let's say I've got a table of all the cities in the world, like this:
country city
------------
Canada Montreal
Cuba Havanna
China Beijing
Canada Victoria
China Macau
I want to count how many cities each country has, so that I would end up with a table as such:
country city_count
------------------
Canada 50
Cuba 10
China 200
I know that I can get the distinct country values with SELECT distinct country FROM T1 and I suspect I need to construct a subquery for the city_count column. But my non-SQL brain is just telling me I need to loop through the results...
Thanks!
Assuming the only reason for a new row is a unique city
select country, count(country) AS City_Count
from table
group by country