How can I find the number of persons from each country
Person table
country_id, fName, lName
Countries table
country_id, country_name
I can find the number of persons from each country with their country IDs, using the below SQL statement
select
p.country_id, COUNT(p.country_id) as [Count]
from
persons p
GROUP BY
p.country_id
But what if I want to fetch country_name instead of country_id?
I tried this so far but it does not work as expected so I am missing something here.
select
c.country_name, COUNT(p.country_id) as [Count]
from
persons p INNER JOIN countries c ON p.country_id = c.country_id
GROUP BY
p.country_id
SQL Server 2000
GROUP BY the columns in the SELECT:
SELECT c.country_name, COUNT(p.country_id) as [Count]
FROM persons p INNER JOIN
countries c
ON p.country_id = c.country_id
GROUP BY c.country_name;
Notes:
Under some circumstances, you would want to include both the id and the name in the GROUP BY -- this would happen if two countries had the same name.
You can use COUNT(*) instead of COUNT(p.country_id). There is no problem counting rows instead of NULL-values.
If you wanted all countries, even those without people, then you would use an outer JOIN:
SELECT c.country_name, COUNT(p.country_id) as [Count]
FROM countries c LEFT JOIN
persons p
ON p.country_id = c.country_id
GROUP BY c.country_name;
You need to mention the column_name which is mentioned in select .
select
c.country_name, COUNT(p.country_id) as [Count]
from
persons p INNER JOIN countries c ON p.country_id = c.country_id
GROUP BY
c.country_name
You could use group by c.country_name .. the column you have in select and you use for refer the group by
select c.country_name, COUNT(p.country_id) as [Count]
from persons p INNER JOIN countries c ON p.country_id = c.country_id
GROUP BY c.country_name
The SQL statement is correct. There was some data corruption in the database due to which the results were not returned correctly.
Related
I need to get clarified the below situation.
I have a city, country table and I need to validate this will some other tables and get the city country results ordered by the country. Here's my query for that
SELECT distinct
c.code as CITY ,
c.country as COUNTRY from location_info li
inner join someTable s on li.loc_id = s.some_id
inner join city c on s.city = c.code
ORDER BY c.country
And this provides the results as
Now when I use OFFSET and LIMIT values in the below query
SELECT distinct
c.code as CITY,
c.country as COUNTRY from location_info li
inner join someTable s on li.loc_id = s.some_id
inner join city c on s.city = c.code
ORDER BY c.country OFFSET 5 ROWS FETCH NEXT 5 ROWS ONLY.
I expect to get ADOR, ADPC, ADSJ, ADVD, ALV as the output.
Why is that and what I am missing here in this query.
When I do the following I get the expected outcome
SELECT CITY, COUNTRY FROM ( SELECT distinct
c.code as CITY,
c.country as COUNTRY from location_info li
inner join someTable s on li.loc_id = s.some_id
inner join city c on s.city = c.code
ORDER BY c.country ) OFFSET 5 ROWS FETCH NEXT 5 ROWS ONLY.
The issue is that the ORDER BY is not stable. What that means is that you have ties in the key values. So, running the query two times might result in different orderings.
This is easily fixed by including more keys in the order by so the order by keys uniquely identify each row:
select distinct c.code as CITY, c.country as COUNTRY
from location_info li join
someTable s
on li.loc_id = s.some_id join
city c
on s.city = c.code
order by c.country, c.code;
I have this SQL query:
SELECT
stu.sno, sname, cname
FROM
sc scc,
(SELECT AVG(sc.grade) AS avg_grade
FROM sc
GROUP BY sc.cno) AS avg_grades
INNER JOIN
course c ON c.cno = scc.cno
INNER JOIN
s stu ON stu.sno = scc.sno;
And there is an error that the multi-part identifier scc.cno could not be bound. I'm confused - could someone help me?
Don't mix implicit and explicit joins! Matter of fact, don't use implicit joins: this is archaic syntax, that should not appear in new code.
The comma in the FROM clause should (probably) be a CROSS JOIN:
SELECT stu.sno, sname, cname
FROM sc scc
CROSS JOIN (SELECT AVG(sc.grade) AS avg_grade FROM sc GROUP BY sc.cno) AS avg_grades
INNER JOIN course c on c.cno = scc.cno
INNER JOIN s stu on stu.sno = scc.sno;
Note that, for this subquery to be useful, you would probably need to select column avg_grade. I would also recommend prefixing each column with the table it belongs to, to remove any possible ambiguity.
Finally: you (probably) can use window functions instead of a subquery:
SELECT stu.sno, sname, cname, scc.
FROM (SELECT *, AVG(grade) OVER() avg_grade FROM sc) scc
INNER JOIN course c on c.cno = scc.cno
INNER JOIN s stu on stu.sno = scc.sno;
Assuming a one-to-many join of students and courses and joined table of student courses (i.e., sc), consider a simplified aggregation on joined tables. Be sure to always qualify columns with alias if query contains more than on table:
SELECT
s.sno AS student_number
, s.sname AS student_name
, c.cname AS course_name
, AVG(sc.grade) AS avg_grade
FROM
sc
INNER JOIN
course c ON c.cno = sc.cno
INNER JOIN
stu s ON s.sno = sc.sno
GROUP BY
s.sno
, s.sname
, c.cname
there is two tables: country , countrylanguage and the common columns are code in country table and countrycode in countrylanguage.
how to retrieve the name of country and count of spoken language in each.
here is what I wrote:
select country.name , countrylanguage.language from country , countrylangauge where countrylanguage.language in (select count(language) from countrylanguage group by countrycode);
If you are using an ANSI compliant database engine (c.f. Wikipedia), you can use JOIN ... ON to join both tables based on the code columns.
SELECT country.name,
count(countrylanguage.language) AS language_count
FROM country
JOIN countrylanguage ON country.code = countrylanguage.countrycode
This performs an inner join, so only the records present in both country and countrylanguagetables will be returned. You can use OUTER JOIN otherwise.
If you are using a database which does not support ANSI joins, the join can be performed in a WHERE clause as follows:
SELECT country.name,
count(countrylanguage.language) AS language_count
FROM country,
countrylanguage
WHERE country.code = countrylanguage.countrycode
Try this following script-
SELECT A.name country_name,
B.language,
COUNT(B.language) total_count
FROM country A
INNER JOIN countrylangauge B ON A.Code = B.countrycode
GROUP BY A.Code
Because you want to take into account that countries could have no languages, you should use a left join:
select c.name, count(cl.language) as num_languages
from country c left join
countrylangauge cl
on cl.countrycode = c.countrycode
group by c.countrycode, c.name;
You appear to be learning SQL. If so, you should not be learning about commas in the FROM clause at all. You should only be learning about JOIN, which is the proper way to join tables together.
I have a table named Actor, with only a column for City (CityId). I want to return the number of actors in a particular State (StateId). The catch however is that I have separate tables for City, County, and finally State (City has CountyId, County has StateId). How do I this in a T-SQL query?
I have a solution that involves nested Select statements, something like:
SELECT COUNT(1)
FROM Actor a
WHERE a.CityId IN
(SELECT CityId FROM City WHERE CountyId IN...)
...but is there a more efficient way to do this? Thanks
You can use this query to get your output
----------------------------------------------------------
SELECT COUNT(ActorId)
FROM Actor a
INNER JOIN City c ON a.cityId = c.cityId
INNER JOIN Country con ON c.countryId = con.countryId
INNER JOIN STATE s ON con.stateId = s.stateId
GROUP BY s.stateId
Use JOINS to query your data.
I am using INNER JOIN here.
Assuming that you have CountryId in your City Table, You can do it following way.
In case you don't have countryId in your City Table you have to apply one more INNER JOIN on State Table.
SELECT COUNT(1) FROM Actor a INNER JOIN
City b ON a.CityId = b.CityId
WHERE b.CountryId IN (...)
You can easily put the JOINS across different table that you have and then use the Group By clause to find out the total number of actors from specific state.
I have used the column name on the basis of my wild guess, you can change them with the original name that you have in your database.
SELECT StateId,
Count(ActorId) AS Total
FROM ACTOR
INNER JOIN City ON Actor.CityId = City.CityId
INNER JOIN County ON County.CountyId = City.CountyId
INNER JOIN State ON State.StateId = County.StateId
GROUP BY State.StateId
Assuming the relation names, you can do something like this with joins:
select s.ID, s.Name, count(*)
from Actors a
inner join Cities c on c.ID = a.CityID
inner join County cn on cn.ID = c.CountyID
inner join State s on s.ID = cn.StateID
group by s.ID, s.Name
If you only need the StateId you don't even need to join with states, this will do:
select cn.StateID, count(*)
from Actors a
inner join Cities c on c.ID = a.CityID
inner join County cn on cn.ID = c.CountyID
group by cn.StateID
I already provide sql fiddle with schema and sample data.
http://sqlfiddle.com/#!2/e9d22/7/0
If I would like to know how many province and how many cities in Thailand.
Country Name | No. Provinces | No. Cities
Thailand | 77 | 1234
I guess that it need to use multiple COUNT(*) but I dont know how to use it.
Anybody know please suggest solution?
You need to use GROUP BY and COUNT:
SELECT c.name, count(distinct p.id) provincecoutn, count(distinct city.id) citycount
FROM country c
LEFT JOIN province p on c.id = p.country_id
LEFT JOIN City on p.id = city.province_id
GROUP BY c.name
Good luck.
Try this:
SELECT
C.Name, COUNT(DISTINCT P.Id) NoProvance, COUNT(CC.Id) NoCities
FROM country C
JOIN province P
ON C.Id = P.COUNTRY_ID
JOIN city CC
ON P.Id = CC.province_id
WHERE C.Name = 'Thailand'
GROUP BY C.Name
SQL FIDDLE DEMO
It's probably faster to count cities per province before joining to province:
SELECT c.name AS "Country Name"
,count(p.id) AS "No. Provinces"
,sum(ci.city_ct) AS "No. Cities"
FROM country c
LEFT JOIN province p ON p.country_id = c.id
LEFT JOIN (
SELECT province_id, count(*) AS city_ct FROM city GROUP BY 1
) ci ON ci.province_id = p.id
GROUP BY 1
-> sqlfiddle for PostgreSQL(!)