Notice: This page requires JavaScript to function properly.
Please enable JavaScript in your browser settings or update your browser.Lære More aggregate statistics! | Grouping
SQL Basics
course content

Kursusindhold

SQL Basics

SQL Basics

1. Selecting
The very first meet with the databaseSELECTing certain columnsLIMITing resultsUnique values from columnUnique values from multiple columnsHow many?How many unique?AliasesTables aliases
2. Filtering
Word filteringNumber filteringCombining conditionsFiltering by numeric intervalMultiple filtering on one columnLIKE filteringNOT like this!
3. Aggregating
MINimal and MAXimal valuesSUMming valuesMean valuesROUNDing
4. Sorting
Sorting by one columnSorting in DESCending orderThe cheapest carSorting by multiple columns
5. Grouping
What is grouping?More aggregate statistics!Grouping by multiple columnsThe cheapest combinationHAVING some conditionsLeast consuming carsFiltering group size
6. Practicing
Challenge: Unique combinationsChallenge: Average Q-series cars priceChallenge: The cheapest new A-series carsChallenge: Relation between engine size and fuel consumptionChallenge: Mileage and manufacture year - is there relation?Challenge: Average price for each model and yearChallenge: The most expensive transmission + engine size combinations

book
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
copy

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.

Opgave

Swipe to start coding

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

Løsning

Switch to desktopSkift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder
Var alt klart?

Hvordan kan vi forbedre det?

Tak for dine kommentarer!

Sektion 5. Kapitel 2
toggle bottom row

book
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
copy

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.

Opgave

Swipe to start coding

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

Løsning

Switch to desktopSkift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder
Var alt klart?

Hvordan kan vi forbedre det?

Tak for dine kommentarer!

Sektion 5. Kapitel 2
Switch to desktopSkift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder
Vi beklager, at noget gik galt. Hvad skete der?
some-alt