Exercise: Looping to add rows into temporary table

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The answer to the exercise will be included and explained if you attend the course listed below!

Category ==> SQL  (192 exercises)
Topic ==> Temporary tables and table variables  (9 exercises)
Level ==> Average difficulty
Course ==> Advanced SQL
Before you can do this exercise, you'll need to download and unzip this file (if you have any problems doing this, click here for help). Once you've done this:
  1. Go into SQL Server Management Studio;
  2. Open the SQL file you've just unzipped (you can press CTRL + O to do this); then
  3. 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).

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The aim of this exercise is to create a temporary table showing the most eventful country for each year. One way to do this is to create a temporary table, and populate its rows within a loop.

Temp Table count events

The first 4 rows out of the 95 years that your query should return.

Note that this is not the only - or even the best - way to do this, but it does provide a useful exercise on temporary tables!

For details of how to proceed, please turn the page!

First write a query to create a temporary table with 3 columns:

Column Contents
Year of events Each year in the database
Country of events The country for that year having most events
Number of events The number of events for this country in this year

Declare variables to hold the earliest and latest event years, and set their values:

YEAR to return only the year of a date

Set the value of your two variables to hold the earliest and latest year referenced in the tblEvent table.

 

Use these variables to start a WHILE loop, which begins at the first year and stops at the last year, adding 1 each time round the loop.

Within your loop, insert one record into your temporary table containing:

  • The current year number (the value of your counter variable within the loop);
  • The country having the most events for this year; and
  • The number of events for this country.

You can get this information by showing the number of events for each country, then adding the TOP 1 clause to pick out just the first country, as ordered by the number of events.

When everything is working, optionally save this exercise as Counting the years away.sql, then close it down.

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