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

Checking for NO Value

When a column doesn't have any value, it's regarded as having a NULL value. To identify whether a value is NULL, we check if it's equal to NULL. Alternatively, the SELECT statement provides a WHERE clause and an IS NULL clause, which is used to examine columns with NULL values.

Let's illustrate this with an example:


              123
            
SELECT name
FROM country
WHERE region IS NULL;

Task

Write an SQL query that returns the name and capital columns with no population.

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

Task

Write an SQL query that returns the name and capital columns with no population.

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

Everything was clear?

Section 3. Chapter 6

Checking for NO Value

Let's illustrate this with an example:


              123
            
SELECT name
FROM country
WHERE region IS NULL;

Task

Write an SQL query that returns the name and capital columns with no population.

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

Task

Write an SQL query that returns the name and capital columns with no population.

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

Everything was clear?

Section 3. Chapter 6

Checking for NO Value

Let's illustrate this with an example:


              123
            
SELECT name
FROM country
WHERE region IS NULL;

Task

Write an SQL query that returns the name and capital columns with no population.

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

Task

Write an SQL query that returns the name and capital columns with no population.

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

Everything was clear?

Let's illustrate this with an example:


              123
            
SELECT name
FROM country
WHERE region IS NULL;

Task

Write an SQL query that returns the name and capital columns with no population.

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

Section 3. Chapter 6

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