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

More aggregate statistics!

Can we calculate more than one aggregate statistic while grouping? Surely we can!

For example, from the audi_cars table, we can calculate the maximum price and tax for each year.


              123
            
SELECT AVG(price) AS "avg_price", AVG(tax) AS "avg_tax", year
FROM audi_cars
GROUP BY year

Please note, while grouping you can put non-aggregated function within SELECT statement only if it figures within GROUP BY, otherwise - it has to be aggregated.

Also note, that in the example above without aliases (AS) there will be two columns with identical names, which is unacceptable in SQL.

Another note: you can use aggregate functions for ordering after GROUP BY statement. It will filter based on calculations within groups.

Завдання

From the audi_cars table find out the minimum and the maximum prices for each model. Sort in descending order by minimum price.

Завдання

From the audi_cars table find out the minimum and the maximum prices for each model. Sort in descending order by minimum price.

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

Все було зрозуміло?

Секція 5. Розділ 2

More aggregate statistics!

Can we calculate more than one aggregate statistic while grouping? Surely we can!

For example, from the audi_cars table, we can calculate the maximum price and tax for each year.


              123
            
SELECT AVG(price) AS "avg_price", AVG(tax) AS "avg_tax", year
FROM audi_cars
GROUP BY year

Please note, while grouping you can put non-aggregated function within SELECT statement only if it figures within GROUP BY, otherwise - it has to be aggregated.

Also note, that in the example above without aliases (AS) there will be two columns with identical names, which is unacceptable in SQL.

Another note: you can use aggregate functions for ordering after GROUP BY statement. It will filter based on calculations within groups.

Завдання

From the audi_cars table find out the minimum and the maximum prices for each model. Sort in descending order by minimum price.

Завдання

From the audi_cars table find out the minimum and the maximum prices for each model. Sort in descending order by minimum price.

Все було зрозуміло?

Секція 5. Розділ 2

More aggregate statistics!

Can we calculate more than one aggregate statistic while grouping? Surely we can!

For example, from the audi_cars table, we can calculate the maximum price and tax for each year.


              123
            
SELECT AVG(price) AS "avg_price", AVG(tax) AS "avg_tax", year
FROM audi_cars
GROUP BY year

Please note, while grouping you can put non-aggregated function within SELECT statement only if it figures within GROUP BY, otherwise - it has to be aggregated.

Also note, that in the example above without aliases (AS) there will be two columns with identical names, which is unacceptable in SQL.

Another note: you can use aggregate functions for ordering after GROUP BY statement. It will filter based on calculations within groups.

Завдання

From the audi_cars table find out the minimum and the maximum prices for each model. Sort in descending order by minimum price.

Завдання

From the audi_cars table find out the minimum and the maximum prices for each model. Sort in descending order by minimum price.

Все було зрозуміло?

Can we calculate more than one aggregate statistic while grouping? Surely we can!

For example, from the audi_cars table, we can calculate the maximum price and tax for each year.


              123
            
SELECT AVG(price) AS "avg_price", AVG(tax) AS "avg_tax", year
FROM audi_cars
GROUP BY year

Please note, while grouping you can put non-aggregated function within SELECT statement only if it figures within GROUP BY, otherwise - it has to be aggregated.

Also note, that in the example above without aliases (AS) there will be two columns with identical names, which is unacceptable in SQL.

Another note: you can use aggregate functions for ordering after GROUP BY statement. It will filter based on calculations within groups.

Завдання

From the audi_cars table find out the minimum and the maximum prices for each model. Sort in descending order by minimum price.

Секція 5. Розділ 2