course content

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

The AVG() FunctionThe AVG() Function

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

AVG() can also determine the average of specific columns or rows (with some conditions). Let's take a look at the following example:

Task

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

Here's a short example of the country table:

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

Everything was clear?

Section 5. Chapter 1
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