Kursusindhold

Introduction to SQL

1. Retrieving Data

Retrieving Individual Columns Retrieving Multiple Columns Retrieving All Columns Retrieving Distinct Rows Limiting Results Challenge: Find the Population of the Countries Challenge: Find All Countries Challenge: Find All Countries With Their IDs Challenge: Find Country Capitals Challenge: Find the Regions in Which All Countries Are Located

2. Sorting Retrieved Data

Sorting Data Challenge: Population Sort Sorting by Multiple Columns Challenge: Dual-Sort Query Specifying Sort Direction Challenge: Sort the Countries by Region and Capital Challenge: Sort Capitals in Descending Order Challenge: Sort Countries in Ascending Order Challenge: Find Countries, Their IDs, and Their Populations Challenge: Find Countries, IDs, Populations, Regions, and Sort Them Challenge: Find All Continents and Sort Them in Ascending Order

3. Filtering Data

Using the WHERE Clause Challenge: North America Population Sort The WHERE Clause Operators Challenge: Population Threshold Query Checking for a Range of Values Checking for NO Value

4. Advanced Data Filtering

Using the AND Operator Challenge: Europe Region Sort Using the OR operator Challenge: America Regions Filter Using the NOT Operator Challenge: Non-Europe Capitals Sort

5. Aggregate Functions

The AVG() Function Challenge: Surface Area Selection The COUNT() Function Challenge: Continental Count The MAX() Function The MIN() Function Challenge: Large Surface Area Average The SUM() Function

Using the WHERE Clause

In databases, tables typically hold substantial volumes of data. However, frequently we're interested in retrieving specific portions of the data rather than the entirety. To accomplish this, we need to define the conditions for data retrieval, which are referred to as filtering criteria.

Data is filtered using a WHERE clause specifying the search criteria in a SELECT statement. The WHERE clause appears immediately after the table name.

When specifying a string value, such as a country name, we need to enclose the text in single quotes (').

Let's see an example:


              123
            
SELECT name, continent 
FROM country 
WHERE continent='Europe';

Explanation: The SELECT statement gets 2 columns from the country table and returns only rows with the continent value 'Europe'.

Clause Position

When we use the ORDER BY and WHERE clauses, we ensure the ORDER BY comes after the WHERE clause.

Let's see the following example:


              1234
            
SELECT capital, continent 
FROM country 
WHERE continent='Asia'
ORDER BY continent DESC;

Here is the country table we are working with:

Opgave

Swipe to start coding

Write an SQL query to retrieve the id, name, and region columns from the country table (please retrieve these columns in this order), returning only rows with the 'North America' continent.

Note

Please note that North America should be correctly capitalized, and north america is not the same. So, be careful and write it as North America.

Løsning

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Sektion 3. Kapitel 1

Using the WHERE Clause

Data is filtered using a WHERE clause specifying the search criteria in a SELECT statement. The WHERE clause appears immediately after the table name.

When specifying a string value, such as a country name, we need to enclose the text in single quotes (').

Let's see an example:


              123
            
SELECT name, continent 
FROM country 
WHERE continent='Europe';

Explanation: The SELECT statement gets 2 columns from the country table and returns only rows with the continent value 'Europe'.

Clause Position

When we use the ORDER BY and WHERE clauses, we ensure the ORDER BY comes after the WHERE clause.

Let's see the following example:


              1234
            
SELECT capital, continent 
FROM country 
WHERE continent='Asia'
ORDER BY continent DESC;

Here is the country table we are working with:

Opgave

Swipe to start coding

Write an SQL query to retrieve the id, name, and region columns from the country table (please retrieve these columns in this order), returning only rows with the 'North America' continent.

Note

Please note that North America should be correctly capitalized, and north america is not the same. So, be careful and write it as North America.

Løsning

Skift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder

Var alt klart?

Tak for dine kommentarer!

Sektion 3. Kapitel 1

Skift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder