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Introduction to SQL
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Introduction to SQL

Introduction to SQL

1. Retrieving Data
Retrieving Individual ColumnsRetrieving Multiple Columns Retrieving All ColumnsRetrieving Distinct RowsLimiting ResultsChallenge: Find the Population of the CountriesChallenge: Find All CountriesChallenge: Find All Countries With Their IDsChallenge: Find Country CapitalsChallenge: Find the Regions in Which All Countries Are Located
2. Sorting Retrieved Data
Sorting DataChallenge: Population SortSorting by Multiple ColumnsChallenge: Dual-Sort QuerySpecifying Sort DirectionChallenge: Sort the Countries by Region and CapitalChallenge: Sort Capitals in Descending OrderChallenge: Sort Countries in Ascending OrderChallenge: Find Countries, Their IDs, and Their PopulationsChallenge: Find Countries, IDs, Populations, Regions, and Sort ThemChallenge: Find All Continents and Sort Them in Ascending Order
3. Filtering Data
Using the WHERE ClauseChallenge: North America Population SortThe WHERE Clause Operators Challenge: Population Threshold QueryChecking for a Range of ValuesChecking for NO Value
4. Advanced Data Filtering
Using the AND OperatorChallenge: Europe Region SortUsing the OR operatorChallenge: America Regions FilterUsing the NOT OperatorChallenge: Non-Europe Capitals Sort
5. Aggregate Functions
The AVG() FunctionChallenge: Surface Area SelectionThe COUNT() FunctionChallenge: Continental CountThe MAX() FunctionThe MIN() FunctionChallenge: Large Surface Area AverageThe SUM() Function

book
The AVG() Function

AVG() returns the average value of a certain column. Let's see an example:


              
12

            
SELECT AVG(population) 
FROM country;
copy

AVG() can also be used to find the average of a selected set of columns or rows that meet certain conditions. Here’s an example:


              
123

            
SELECT AVG(population) 
FROM country
WHERE population < 4478500;
copy

Here is the country table we are working with:

Opgave

Swipe to start coding

Write an SQL query to retrieve the average value of a surfacearea column from the country table.

Løsning

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Var alt klart?

Hvordan kan vi forbedre det?

Tak for dine kommentarer!

Sektion 5. Kapitel 1
toggle bottom row

book
The AVG() Function

AVG() returns the average value of a certain column. Let's see an example:


              
12

            
SELECT AVG(population) 
FROM country;
copy

AVG() can also be used to find the average of a selected set of columns or rows that meet certain conditions. Here’s an example:


              
123

            
SELECT AVG(population) 
FROM country
WHERE population < 4478500;
copy

Here is the country table we are working with:

Opgave

Swipe to start coding

Write an SQL query to retrieve the average value of a surfacearea column from the country table.

Løsning

Switch to desktopSkift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder
Var alt klart?

Hvordan kan vi forbedre det?

Tak for dine kommentarer!

Sektion 5. Kapitel 1
Switch to desktopSkift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder
Vi beklager, at noget gik galt. Hvad skete der?
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