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Software ==>	SQL (203 exercises)
Topic ==>	Aggregation and grouping (12 exercises)
Level ==>	Harder than average
Subject ==>	SQL training

Use a complex CASE statement to show the number of events for each century, including the CUBE function

This exercise is provided to allow potential course delegates to choose the correct Wise Owl Microsoft training course, and may not be reproduced in whole or in part in any format without the prior written consent of Wise Owl.

Before you can do this exercise, you'll need to download and unzip this file . Once you've done this:

Go into SQL Server Management Studio;
Open the SQL file you've just unzipped (you can press CTRL + O to do this); then
Execute this script.

This will generate the database that you'll need to use in order to do this exercise (note that the database and script are only to be used for exercises published on this website, and may not be reused or distributed in any form without the prior written permission of Wise Owl).

Create a query to show the following information:

You'll need to calculate the century for each event date, and group by this.

To get the top row giving the grand total in the same query, encase your GROUP BY expression in the CUBE function.

Save this query as Passing of the centuries, 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.

You can find other training resources for the subject of this exercise here:

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From:	Bhavya59
When:	01 Aug 24 at 13:48

SELECT CASE

WHEN EventDate>='1701-01-01' AND EventDate<'1801-01-01' THEN '18th Century'

WHEN EventDate>='1801-01-01' AND EventDate<'1901-01-01' THEN '19th Century'

WHEN EventDate>='1901-01-01' AND EventDate<'2001-01-01' THEN '20th Century'

WHEN EventDate>='2001-01-01' THEN '21th Century'

ELSE ''

END AS Century

,COUNT(EventID)

FROM tblEvent

GROUP BY CUBE((CASE

WHEN EventDate>='1701-01-01' AND EventDate<'1801-01-01' THEN '18th Century'

WHEN EventDate>='1801-01-01' AND EventDate<'1901-01-01' THEN '19th Century'

WHEN EventDate>='1901-01-01' AND EventDate<'2001-01-01' THEN '20th Century'

WHEN EventDate>='2001-01-01' THEN '21th Century'

ELSE ''

END))

From:	roqovzki
When:	12 Feb 24 at 23:13

So, this is my pretty simple or maybe even dumb query (as I'm a beginner), but I came across this exercise and it seems to me that the solution given in the files and most of the users replies are incorrect.

I belivee most of the solutions miss out on one year of each century, as the century lasts from XX01-01-01 till XX00-12-31.
Let me know guys whether I'm completely missing on something.

SELECT

COUNT(*)

,CASE

WHEN EventDate BETWEEN '1701-01-01' AND '1800-12-31' THEN '18th century'

WHEN EventDate BETWEEN '1801-01-01' AND '1900-12-31' THEN '19th century'

WHEN EventDate BETWEEN '1901-01-01' AND '2000-12-31' THEN '20th century'

WHEN EventDate BETWEEN '2001-01-01' AND '2100-12-31' THEN '21th century'

END AS [Century]

FROM

tblEvent

GROUP BY CUBE

(CASE

WHEN EventDate BETWEEN '1701-01-01' AND '1800-12-31' THEN '18th century'

WHEN EventDate BETWEEN '1801-01-01' AND '1900-12-31' THEN '19th century'

WHEN EventDate BETWEEN '1901-01-01' AND '2000-12-31' THEN '20th century'

WHEN EventDate BETWEEN '2001-01-01' AND '2100-12-31' THEN '21th century'

END)

--------------------------------------------------------
WiseOwl query I believe should be like this:

SELECT

-- derive the century

CASE

WHEN year(e.EventDate) < 1801 THEN '18th century'

WHEN year(e.EventDate) < 1901 THEN '19th century'

WHEN year(e.EventDate) < 2001 THEN '20th century'

ELSE '21st century'

END AS Century,

COUNT(*) AS 'Number events'

FROM

tblEvent AS e

GROUP BY

-- need to group by the century too (the CUBE function shows the grand total too)

CUBE(

CASE

WHEN year(e.EventDate) < 1801 THEN '18th century'

WHEN year(e.EventDate) < 1901 THEN '19th century'

WHEN year(e.EventDate) < 2001 THEN '20th century'

ELSE '21st century'

END

)

ORDER BY

Century

From:	Rupchand7
When:	14 Nov 23 at 07:18

select
   case when datepart(year,eventdate) like '17%' then '18th century'
   when datepart(year,eventdate) like '18%' then '19th century'
   when datepart(year,eventdate) like '19%' then '20th century'
   else '21th century'
   end as century, count(eventid) as [Number of Events] from tblEvent group by
   cube( case when datepart(year,eventdate) like '17%' then '18th century'
   when datepart(year,eventdate) like '18%' then '19th century'
   when datepart(year,eventdate) like '19%' then '20th century'
   else '21th century'
   end) order by century

From:	4mj4d
When:	13 Aug 23 at 13:35

select
CAST(CAST(left(EventDate, 2) as int) + 1 as varchar)+ 'th century' as [Number of events],
COUNT(left(EventDate, 2))
from tblEvent
GROUP BY CUBE(left(EventDate, 2))
ORDER BY [Number of events]

From:	mvh_analyst
When:	15 Dec 22 at 09:20

Didn't see this as a solution yet:

select concat((year(EventDate) / 100) + 1,'th century') as century,
count(*) as [Number of events]
from tblEvent
group by concat((year(EventDate) / 100) + 1,'th century')

From:	linjom
When:	23 Apr 18 at 07:33

I am getting different result..

NULL   459
18th Century   4
19th Century   14
20th Century   396
21st Century   45

for both rollup and cube.. is this right? Final total same as site.

From:	Zerish
When:	22 May 18 at 05:43

This will give you exact same result as posted on site

USE WorldEvents
GO

SELECT
CASE
WHEN DATEPART(YY,tblEvent.EventDate) like '18%' THEN '19th Century'
WHEN DATEPART(YY,tblEvent.EventDate) like '17%' THEN '18th Century'
WHEN DATEPART(YY,tblEvent.EventDate) like '19%' THEN '20th Century'
WHEN DATEPART(YY,tblEvent.EventDate) like '20%' THEN '21st Century'
END AS Century,COUNT(tblEvent.EventName) AS NumberOfEvents
FROM tblEvent
GROUP BY CUBE(CASE
WHEN DATEPART(YY,tblEvent.EventDate) like '18%' THEN '19th Century'
WHEN DATEPART(YY,tblEvent.EventDate) like '17%' THEN '18th Century'
WHEN DATEPART(YY,tblEvent.EventDate) like '19%' THEN '20th Century'
WHEN DATEPART(YY,tblEvent.EventDate) like '20%' THEN '21st Century'
END)
ORDER BY NumberOfEvents DESC

From:	ShukiMolk
When:	12 Apr 20 at 16:55

This is way too specific. What will happen once more event are updated to the database? And there might be events from before the 18th century.

I believe we should write a code that can be used over more data.

How about this:

SELECT
(CAST(((YEAR(EventDate)/100)+1) AS varchar) + 'th century') AS 'Century',
COUNT(CAST(((YEAR(EventDate)/100)+1) AS varchar) + 'th century') AS 'Number of events'
FROM
[tblEvent]
GROUP BY
(CAST(((YEAR(EventDate)/100)+1) AS varchar) + 'th century')
WITH CUBE

From:	SeahawkZim
When:	22 Mar 20 at 00:09

Hi, I would like to offer these observations by using the code below:

use worldevents
go
SELECT CASE LEFT(CONVERT(VARCHAR(10), eventdate, 121), 2) WHEN '20' THEN '21st century'
               WHEN '19' THEN '20th century'
               WHEN '18' THEN '19th century'
               WHEN '17' THEN '18th century' end as Century,
COUNT(eventid) AS [Number of Events]
FROM tblevent
GROUP BY CUBE (CASE LEFT(CONVERT(VARCHAR(10), eventdate, 121), 2) WHEN '20' THEN '21st century'
                   WHEN '19' THEN '20th century'
                   WHEN '18' THEN '19th century'
                   WHEN '17' THEN '18th century' end)
ORDER BY Century

Using a simple CASE construct, makes the code easier to read. Grouping on the eventid (primary key) ensures an accurate count. Grouping on the eventname (nullable) doesn't ensure you will get an accurate count. Also, using an explicit conversion avoids the sql engine from having to do an implicit conversion from date to string so that the LIKE statement can be used. Also, LIKE and wildcards are usually a drag on performance but in this case with only a few rows, the hit is not noticeable. In the actual performance plan, the buffer size using this code is 1/4 the size of the code using LIKE. Going up against a lot of data could produce a memory hit.

From:	Andy B
When:	23 Mar 20 at 09:50

Impressive analysis - thanks!

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EXERCISE TOPIC

SQL EXERCISES

SQL EXERCISES

Use a complex CASE statement to show the number of events for each century, including the CUBE function

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