Introduction to SQL

1. Retrieving Data

In this section, we will learn how to use the SQL SELECT statement to get a single table column, multiple table columns, and all table columns. We will also find out how to return unique values.

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

In this section, we will learn how to sort retrieved data using the ORDER BY clause. This clause, which must be the last in the SELECT statement, can be used to sort data on one or more columns as needed.\n

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

In this section, we will learn how to filter returned data using the SELECT statement’s WHERE clause. We will learn how to test for equality, inequality, more and less significant than value ranges, and NULL values.

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

In this section, we will learn how to combine WHERE clauses with the AND and OR operators. We will also find out how the NOT operator works.\n\n\n

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

In this section, we will learn what the SQL aggregate functions are and how to use them to summarize table data.

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:

Завдання

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

Все було зрозуміло?

Секція 3. Розділ 6

Зміст курсу

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

Checking for NO Value

Let's illustrate this with an example:

Завдання

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

Все було зрозуміло?

Секція 3. Розділ 6