Зміст курсу

SQL Basics

1. Selecting

The very first meet with the database SELECTing certain columns LIMITing results Unique values from column Unique values from multiple columns How many?How many unique?Aliases Tables aliases

2. Filtering

Word filtering Number filtering Combining conditions Filtering by numeric interval Multiple filtering on one column LIKE filtering NOT like this!

3. Aggregating

MINimal and MAXimal values SUMming values Mean values ROUNDing

4. Sorting

Sorting by one column Sorting in DESCending order The cheapest car Sorting by multiple columns

5. Grouping

What is grouping?More aggregate statistics!Grouping by multiple columns The cheapest combination HAVING some conditions Least consuming cars Filtering group size

6. Practicing

Challenge: Unique combinations Challenge: Average Q-series cars price Challenge: The cheapest new A-series cars Challenge: Relation between engine size and fuel consumption Challenge: Mileage and manufacture year - is there relation?Challenge: Average price for each model and year Challenge: The most expensive transmission + engine size combinations

Unique values from multiple columns

But what if we want to know, for example, unique pairs 'country-city' of our site visitors? Surely, we can extract unique countries (like in the previous chapter) and unique cities. But then we have to connect each city to the country manually.

This task can be solved by the same DISTINCT, but this time with two columns. For example,


              12
            
SELECT DISTINCT(country), city
FROM visitors

The DISTINCT statement will return all the unique combinations of columns you chose. Using parentheses is not mandatory, i.e. you for the example above you can write DISTINCT country, city. But placing multiple columns within DISTINCT parentheses will return only one column of all unique combinations in (country, city) format.

Завдання

Extract all unique combinations of model and transmission

Завдання

Extract all unique combinations of model and transmission

Перейдіть на комп'ютер для реальної практикиПродовжуйте з того місця, де ви зупинились, використовуючи один з наведених нижче варіантів

Все було зрозуміло?

Секція 1. Розділ 5

Unique values from multiple columns

This task can be solved by the same DISTINCT, but this time with two columns. For example,


              12
            
SELECT DISTINCT(country), city
FROM visitors

The DISTINCT statement will return all the unique combinations of columns you chose. Using parentheses is not mandatory, i.e. you for the example above you can write DISTINCT country, city. But placing multiple columns within DISTINCT parentheses will return only one column of all unique combinations in (country, city) format.

Завдання

Extract all unique combinations of model and transmission

Завдання

Extract all unique combinations of model and transmission

Все було зрозуміло?

Секція 1. Розділ 5

Unique values from multiple columns

This task can be solved by the same DISTINCT, but this time with two columns. For example,


              12
            
SELECT DISTINCT(country), city
FROM visitors

The DISTINCT statement will return all the unique combinations of columns you chose. Using parentheses is not mandatory, i.e. you for the example above you can write DISTINCT country, city. But placing multiple columns within DISTINCT parentheses will return only one column of all unique combinations in (country, city) format.

Завдання

Extract all unique combinations of model and transmission

Завдання

Extract all unique combinations of model and transmission

Все було зрозуміло?

This task can be solved by the same DISTINCT, but this time with two columns. For example,


              12
            
SELECT DISTINCT(country), city
FROM visitors

The DISTINCT statement will return all the unique combinations of columns you chose. Using parentheses is not mandatory, i.e. you for the example above you can write DISTINCT country, city. But placing multiple columns within DISTINCT parentheses will return only one column of all unique combinations in (country, city) format.

Завдання

Extract all unique combinations of model and transmission

Секція 1. Розділ 5