Course Content

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

Specifying Sort Direction

We can sort data in more than just ascending order, which is the default sort order. The ORDER BY clause can sort the data in descending order, and to do this, we need to specify the keyword DESC. Let's look at an example:


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SELECT continent 
FROM country 
ORDER BY continent DESC;

Sorting Multiple Columns in Descending Order

We can sort the data by multiple columns. In fact, it is often necessary to sort data by more than one column. For instance, when displaying a list of students, we may want to display it sorted by last name and first name. This kind of sorting is useful when multiple students share the same name. When sorting in descending order on multiple columns, each column should have its own DESC keyword. Let's see an example.


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

Explanation: The DESC keyword must only be applied to the column's name we want to sort in descending order. In our example, DESC was specified for the name column but not for the region column. Therefore, the name column is sorted in descending order, but the region column is sorted in ascending order (ascending order is the default).

Task

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.

Here's a short example of the country table:

id	name	continent	region	surfacearea	capital	population
1	Japan	Asia	Eastern Asia	377829	Tokyo	126714000
2	Latvia	Europe	NULL	64589	Riga	2424200
3	Mexico	North America	Central America	1958201	Mexico City	98881000
...	...	...	...	...	...	...
15	Malta	Europe	Southern Europe	316	Valletta	380200

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Section 2. Chapter 5

Specifying Sort Direction


              123
            
SELECT continent 
FROM country 
ORDER BY continent DESC;

Sorting Multiple Columns in Descending Order


              123
            
SELECT id, name, region 
FROM country 
ORDER BY region, name DESC;

Task

Here's a short example of the country table:

id	name	continent	region	surfacearea	capital	population
1	Japan	Asia	Eastern Asia	377829	Tokyo	126714000
2	Latvia	Europe	NULL	64589	Riga	2424200
3	Mexico	North America	Central America	1958201	Mexico City	98881000
...	...	...	...	...	...	...
15	Malta	Europe	Southern Europe	316	Valletta	380200

Switch to desktop for real-world practiceContinue from where you are using one of the options below

Everything was clear?

Thanks for your feedback!

Section 2. Chapter 5

Specifying Sort Direction


              123
            
SELECT continent 
FROM country 
ORDER BY continent DESC;

Sorting Multiple Columns in Descending Order


              123
            
SELECT id, name, region 
FROM country 
ORDER BY region, name DESC;

Task

Here's a short example of the country table:

id	name	continent	region	surfacearea	capital	population
1	Japan	Asia	Eastern Asia	377829	Tokyo	126714000
2	Latvia	Europe	NULL	64589	Riga	2424200
3	Mexico	North America	Central America	1958201	Mexico City	98881000
...	...	...	...	...	...	...
15	Malta	Europe	Southern Europe	316	Valletta	380200

Switch to desktop for real-world practiceContinue from where you are using one of the options below

Everything was clear?

Thanks for your feedback!


              123
            
SELECT continent 
FROM country 
ORDER BY continent DESC;

Sorting Multiple Columns in Descending Order


              123
            
SELECT id, name, region 
FROM country 
ORDER BY region, name DESC;

Task

Here's a short example of the country table:

id	name	continent	region	surfacearea	capital	population
1	Japan	Asia	Eastern Asia	377829	Tokyo	126714000
2	Latvia	Europe	NULL	64589	Riga	2424200
3	Mexico	North America	Central America	1958201	Mexico City	98881000
...	...	...	...	...	...	...
15	Malta	Europe	Southern Europe	316	Valletta	380200

Switch to desktop for real-world practiceContinue from where you are using one of the options below

Section 2. Chapter 5

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