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

Introduction to SQL

Limiting Results

We know that the SELECT operator can retrieve all rows from a table of all or the 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.

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
4	Netherlands	Europe	Western Europe	41526	Amsterdam	15864000
...	...	...	...	...	...	...
15	Malta	Europe	Southern Europe	316	Valletta	380200

Task

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

Everything was clear?

Section 1. Chapter 5

Course Content

Introduction to SQL

1. Retrieving Data

2. Sorting Retrieved Data

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

Introduction to SQL

Limiting Results

We know that the SELECT operator can retrieve all rows from a table of all or the 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.

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
4	Netherlands	Europe	Western Europe	41526	Amsterdam	15864000
...	...	...	...	...	...	...
15	Malta	Europe	Southern Europe	316	Valletta	380200

Task

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

Everything was clear?

Section 1. Chapter 5