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

How many unique?

But what if we want to calculate the number of unique site visitors? Sounds like a combination of selecting unique and then counting...

Yes, that's the point! To calculate the number of unique observations over a certain column use COUNT(DISTINCT( ... )) statement. For example,


              12
            
SELECT COUNT(DISTINCT(user_id))
FROM visitors

This query will return a single value - the number of unique user_id in the visitors table.

Завдання

Count the number of different cars models in the audi_cars table.

Завдання

Count the number of different cars models in the audi_cars table.

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 7

How many unique?

But what if we want to calculate the number of unique site visitors? Sounds like a combination of selecting unique and then counting...

Yes, that's the point! To calculate the number of unique observations over a certain column use COUNT(DISTINCT( ... )) statement. For example,


              12
            
SELECT COUNT(DISTINCT(user_id))
FROM visitors

This query will return a single value - the number of unique user_id in the visitors table.

Завдання

Count the number of different cars models in the audi_cars table.

Завдання

Count the number of different cars models in the audi_cars table.

Все було зрозуміло?

Секція 1. Розділ 7

How many unique?

But what if we want to calculate the number of unique site visitors? Sounds like a combination of selecting unique and then counting...

Yes, that's the point! To calculate the number of unique observations over a certain column use COUNT(DISTINCT( ... )) statement. For example,


              12
            
SELECT COUNT(DISTINCT(user_id))
FROM visitors

This query will return a single value - the number of unique user_id in the visitors table.

Завдання

Count the number of different cars models in the audi_cars table.

Завдання

Count the number of different cars models in the audi_cars table.

Все було зрозуміло?

But what if we want to calculate the number of unique site visitors? Sounds like a combination of selecting unique and then counting...

Yes, that's the point! To calculate the number of unique observations over a certain column use COUNT(DISTINCT( ... )) statement. For example,


              12
            
SELECT COUNT(DISTINCT(user_id))
FROM visitors

This query will return a single value - the number of unique user_id in the visitors table.

Завдання

Count the number of different cars models in the audi_cars table.

Секція 1. Розділ 7