given that there are 2 such entities
city(name, country, population)
country(code, name, capital, population)
and the question is that there exist cities in different countries that have the same name. For instance, paris in texas, usa, and paris in france. we assume, however, that every city in one country has a unique name in that country. find the names of cities that have a unique name.
would this work then
SELECT DISTINCT c1.name
FROM city c1, city c2
WHERE c1.name<>c2.name;
This will find all the cities that are unique in the database.
SELECT name
FROM city
Group by city
Having count(city) = 1
Related
I would like to get every country out of Mondial database that has only cities that start with "A".
I already have the amount of cities each country has and the amount of cities each country has that start with an "A". My idea was to just compare the numbers of the count statement but I don't know how to compare 2 queries that are grouped.
The following tables are interesting for that task if you don't know about mondial.
City: Name, Country, Province, Population
Country: Name, Code, Capital, Area, Population
My queries were the following:
SELECT Country.Code, Count(City.Name)
FROM City,
Country
WHERE Country.Code = City.Country
AND City.Name LIKE 'A%'
GROUP BY Country.Name
And the query without LIKE = 'A%'
I hope you can help me.
As suggested by #jarlh I would use NOT EXISTS
SELECT Country.Code
FROM Country
WHERE NOT EXISTS (
SELECT 1
FROM City
WHERE Country.Code = City.Country
AND City.Name NOT LIKE 'A%'
)
I need to identify rows where a certain value is repeated. Here is a sample table:
COUNTRY CITY
Italy Milan
Englad London
USA New York
Canada London
USA Atlanta
The query should return...
COUNTRY CITY
Englad London
Canada London
...because London is repeated. Thank you in advance for your help.
The easiest way is to use a subquery that counts the number of times each city appears (and filter to those values that appear more than once):
SELECT * FROM Cities
WHERE City in
(
SELECT City FROM Cities
GROUP BY City
HAVING COUNT(*) > 1
)
If your DBMS supports windowed aggregates.
SELECT COUNTRY,
CITY
FROM (SELECT COUNTRY,
CITY,
COUNT(*) OVER (PARTITION BY CITY) AS Cnt
FROM Cities) T
WHERE Cnt > 1
SQL Fiddle
select country, city
from aTable
where city in
(
select city
from aTable
group by city
HAVING count(1) > 1
)
Try it here: http://sqlfiddle.com/#!3/e9b1a/1
Or if the same city & country combo appears twice and you're only interested where the countries are different:
select distinct country, city
from aTable
where city in
(
select city
from aTable
group by city
HAVING count(distinct country) > 1
)
Try it here: http://sqlfiddle.com/#!3/2dfaa/2
This one works. Got it from my wife (she finally had time to look into this). Thought you might be interested.
SELECT * FROM Cities
WHERE City in ( select city
from (SELECT City,
count(distinct country)
FROM Cities
GROUP BY City
HAVING count(distinct country) > 1) a )
I'm trying to count the occurrences of a distinct set of cities and countries in a user table.
The table is set out similar to:
userid city country
------ --------- --------------
1 Cambridge United Kingdom
2 London United Kingdom
3 Cambridge United Kingdom
4 New York United States
What I need is a list of every city, country pair with the number of occurrences:
Cambridge, United Kingdom, 2
London, United Kingdom, 1
New York, United States, 1
Currently I run an SQL query to get the distinct pairs:
$array = SELECT DISTINCT city, country FROM usertable
then read it into an array in PHP, and loop through the array, running a query to count each occurrences for each row in the array:
SELECT count(*) FROM usertable
WHERE city = $array['city']
AND country = $array['country']
I'm assuming my scant grasp of SQL is missing something - what would be the correct way to do this, preferably without the intervention of PHP?
select city, country, count(*)
from usertable
group by city, country
What you need is a group by:
Select city, country, count(*) as counter
from usertable
group by city, country
SELECT cityandcountry, count(*) as occurrences FROM (
SELECT DISTINCT concat(city, country) FROM tablename
) as baseview;
if you want city and country preformated, or
SELECT cityandcountry, count(*) as occurrences FROM (
SELECT DISTINCT city, country FROM tablename
) as baseview;
if not.
I have the following table that contains the following data:
http://img513.imageshack.us/img513/9039/mycities.png
The CREATE statement and the inserts are at http://snipt.org/xoKl .
The table is a list of cities and each city belongs to a region and a country and each city has a founding date. The goal here is to get for each "Country / Region" pair a list of the oldest cities. We need the oldest city on the east coast of Canada, the oldest city on the west coast of the U.S and so on ...
The query that I use right now is:
SELECT * FROM MyCities
INNER JOIN
(SELECT Country, Region, MIN(FoundingDate) AS CityFoundingDate
FROM MyCities
GROUP BY Country, Region ) AS subquery
ON subquery.CityFoundingDate = MyCities.FoundingDate
AND MyCities.Country = subquery.Country
AND MyCities.Region = subquery.Region
I just want to know whether there are other ways to write this group by query or not. :-)
Is this query efficient or not?
Looking forward to a discussion.
What about?
select country, region, city from MyCities mc1
where foundingDate <= ALL (
select foundingDate from MyCities as mc2
where mc1.country = mc2.country and mc1.region = mc2.region
)
How about something like this?
Should work in Oracle (although I can't test it right now)
SELECT country, region, city, foundingdate
FROM (
SELECT country, region, city, foundingdate, MIN(founding_date) OVER PARTITION BY (country, region) min_date
FROM mycities) WHERE foundingdate=min_date
But what if there are two cities founded on the same year in the same country/region?
I currently am making a dynamic query string that is comprised of whatever a user checks on a html form. There is Country, District, Population, and Language.
When I select Country, District, and Population the query string SELECT Country, District, Population FROM City WHERE name ='Tulsa' is created. The problem is Country is in a different table.
How do I read from the City table and the Country table in the same query string?
Assuming both your City and Country tables have a CountryID; try this:
SELECT Country, District, Population
FROM City
INNER JOIN Country ON Country.CountryID = City.CountryID
WHERE City.name = 'Tulsa';