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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
Retrieving Distinct Rows

Note that the SELECT statement returns all rows in a given column. However, what if we don't need all the values from a column, especially when they are duplicated, and we only need unique values?

For such cases, it is convenient to use the keyword DISTINCT, placed immediately before the column names. Let's take a look at an example:


              
12

            
SELECT DISTINCT region 
FROM country;
copy

Here's a short example of the country table:

Opgave

Swipe to start coding

Write an SQL query to retrieve distinct (unique) continent values from the country table.

Løsning

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Var alt klart?

Hvordan kan vi forbedre det?

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Sektion 1. Kapitel 4
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book
Retrieving Distinct Rows

Note that the SELECT statement returns all rows in a given column. However, what if we don't need all the values from a column, especially when they are duplicated, and we only need unique values?

For such cases, it is convenient to use the keyword DISTINCT, placed immediately before the column names. Let's take a look at an example:


              
12

            
SELECT DISTINCT region 
FROM country;
copy

Here's a short example of the country table:

Opgave

Swipe to start coding

Write an SQL query to retrieve distinct (unique) continent values 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 1. Kapitel 4
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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