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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:

Tehtävä

Swipe to start coding

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

Ratkaisu

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Kiitos palautteestasi!

Osio 1. Luku 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:

Tehtävä

Swipe to start coding

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

Ratkaisu

Switch to desktopVaihda työpöytään todellista harjoitusta vartenJatka siitä, missä olet käyttämällä jotakin alla olevista vaihtoehdoista
Oliko kaikki selvää?

Miten voimme parantaa sitä?

Kiitos palautteestasi!

Osio 1. Luku 4
Switch to desktopVaihda työpöytään todellista harjoitusta vartenJatka siitä, missä olet käyttämällä jotakin alla olevista vaihtoehdoista
Pahoittelemme, että jotain meni pieleen. Mitä tapahtui?
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