SQL | Subqueries exercise | Show countries with more than 8 events, using a subquery

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Software ==> SQL  (198 exercises)
Version ==> Any version of SQL Server
Topic ==> Subqueries  (5 exercises)
Level ==> Average difficulty
Course ==> Introduction to SQL
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Write a query which lists out countries which have more than 8 events, using a correlated subquery rather than HAVING. 

That is: list the names of countries from the countries table where for each country the number of events matching the country's id is more than 8.

If you list the countries in alphabetical order, you should get:

Countries with events

Although your query should be easy to read, one disadvantage is that you can't see how many events there were for each country.

 

Save this query as Eventful countries, then close it down.

You can unzip this file to see the answers to this exercise, although please remember this is for your personal use only.
This page has 3 threads Add post
Anita   Reply to AnitaReply
27 Jun 20 at 17:55

We can get the country name and no of event occured  without even using a subquery:

select distinct count([EventName]) as No_of_event,[CountryName] from [tblEvent] e
inner join [dbo].[tblCountry]  c on e.CountryID = c.CountryID
group by [CountryName]
having count([EventName]) >8

mgroesink   Reply to mgroesinkReply
11 Jun 20 at 15:56

Not a big deal to show also the numbers of events per country:

select c.CountryName , (select count(*)    from tblEvent where CountryID = C.CountryID) [Number of events]
from tblCountry c

ShukiMolk   Reply to ShukiMolkReply
12 Apr 20 at 23:38

Couldn't do it without using HAVING in the subquery :-(
Anyone has any ideas?

DISTINCT cntr.CountryName
FROM
    tblEvent evnt
    INNER JOIN tblCountry cntr
    ON evnt.CountryID = cntr.CountryID
WHERE evnt.CountryID IN
--countryID for countries that has more than 8 events
        (
        SELECT
        evnt.CountryID
        --,count(evnt.EventID) AS [Number of events]
        FROM
            tblEvent evnt
            INNER JOIN tblCountry cntr
            ON evnt.CountryID = cntr.CountryID
        GROUP BY
        evnt.CountryID,
        cntr.CountryName
        Having
        count(evnt.EventID) > 8
        )

Thomas   Reply to ThomasReply
16 Apr 20 at 18:01

Hi,

Looks like this is working:

SELECT 
    c.CountryName
FROM
    tblCountry c
WHERE
    8 < (
        SELECT
            COUNT(e.EventID)
        FROM
            tblEvent e
        WHERE
            e.CountryID = c.CountryID
    )
Order By
    c.CountryName;

ShukiMolk   Reply to ShukiMolkReply
21 Apr 20 at 16:44

Got it.
Tnx

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