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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
Specifying Sort Direction

Sorting Columns in Descending Order

We can do more than just sort data in ascending order by default. The ORDER BY clause can also arrange data in descending order, which requires using the DESC keyword.

Let's look at an example:


              
123

            
SELECT continent 
FROM country 
ORDER BY continent DESC;
copy

Sorting Multiple Columns in Descending Order

We can sort data by multiple columns, and in many cases, this is actually necessary. For example, when displaying a list of students, you might want to order them first by their last name and then by their first name. This approach is especially helpful when multiple students share the same name.

Also, if you’re sorting in descending order by more than one column, remember that each column must include its own DESC keyword.

Let's see an example.


              
123

            
SELECT id, name, region 
FROM country 
ORDER BY region, name DESC;
copy

Explanation: You only need to apply the DESC keyword to the column you want sorted in descending order. In our example, we used DESC for the name column but not for the region column. As a result, the name column is sorted in descending order, while the region column remains sorted in ascending order (the default).

Here is the country table we are working with:

Uppgift

Swipe to start coding

Write an SQL query to retrieve five columns using the SELECT statement, namely: name, continent, region, population, and capital (please retrieve these columns in this order). Sort the result by two of them: first by continent in descending order, then by population in ascending order.

Lösning

Switch to desktopByt till skrivbordet för praktisk övningFortsätt där du är med ett av alternativen nedan
Var allt tydligt?

Hur kan vi förbättra det?

Tack för dina kommentarer!

Avsnitt 2. Kapitel 5
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book
Specifying Sort Direction

Sorting Columns in Descending Order

We can do more than just sort data in ascending order by default. The ORDER BY clause can also arrange data in descending order, which requires using the DESC keyword.

Let's look at an example:


              
123

            
SELECT continent 
FROM country 
ORDER BY continent DESC;
copy

Sorting Multiple Columns in Descending Order

We can sort data by multiple columns, and in many cases, this is actually necessary. For example, when displaying a list of students, you might want to order them first by their last name and then by their first name. This approach is especially helpful when multiple students share the same name.

Also, if you’re sorting in descending order by more than one column, remember that each column must include its own DESC keyword.

Let's see an example.


              
123

            
SELECT id, name, region 
FROM country 
ORDER BY region, name DESC;
copy

Explanation: You only need to apply the DESC keyword to the column you want sorted in descending order. In our example, we used DESC for the name column but not for the region column. As a result, the name column is sorted in descending order, while the region column remains sorted in ascending order (the default).

Here is the country table we are working with:

Uppgift

Swipe to start coding

Write an SQL query to retrieve five columns using the SELECT statement, namely: name, continent, region, population, and capital (please retrieve these columns in this order). Sort the result by two of them: first by continent in descending order, then by population in ascending order.

Lösning

Switch to desktopByt till skrivbordet för praktisk övningFortsätt där du är med ett av alternativen nedan
Var allt tydligt?

Hur kan vi förbättra det?

Tack för dina kommentarer!

Avsnitt 2. Kapitel 5
Switch to desktopByt till skrivbordet för praktisk övningFortsätt där du är med ett av alternativen nedan
Vi beklagar att något gick fel. Vad hände?
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