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Course Content

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 DataChallengeSorting by Multiple ColumnsChallengeSpecifying 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 ClauseChallengeThe WHERE Clause Operators ChallengeChecking for a Range of ValuesChecking for NO Value

4. Advanced Data Filtering

Using the AND OperatorChallengeUsing the OR operatorChallengeUsing the NOT OperatorChallenge

5. Aggregate Functions

The AVG() FunctionChallengeThe COUNT() FunctionChallengeThe MAX() FunctionThe MIN() FunctionChallengeThe SUM() Function

Introduction to SQL

Limiting ResultsLimiting Results

We know that the SELECT operator can retrieve all rows from a table or specific columns. However, what if we only need to fetch a specific number of rows?

Note

This can be achieved using different syntax in various database management systems. In our case, since we are using PostgreSQL, we should utilize the LIMIT clause.

In the example below, we extract the first 7 rows (in our case, the capitals of the countries) from the column.

Task

From the ' country ' table, let's retrieve 3 distinct (unique) continent values.

Here's a short example of the country table:

idnamecontinentregionsurfaceareacapitalpopulation
1JapanAsiaEastern Asia377829Tokyo126714000
2LatviaEuropeNULL64589Riga2424200
3MexicoNorth AmericaCentral America1958201Mexico City98881000
.....................
15MaltaEuropeSouthern Europe316Valletta380200

Everything was clear?

Section 1. Chapter 5
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