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SQL Basics
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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
How many?

What if you want to know the exact number of observations in your database? Counting manually sounds like a very very bad idea.

Fortunately, SQL has the built-in functionality of counting rows. To count the number of rows in the whole dataset use COUNT *. For example, we can count the total number of our website being visited by using the following query:


              
12

            
SELECT COUNT(*)
FROM visitors
copy

Please note, that for counting the total number of rows you must place * within parenthesis, like COUNT(*).

Opgave

Swipe to start coding

Count number of Audi cars sold from audi_cars table.

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 1. Kapitel 6
toggle bottom row

book
How many?

What if you want to know the exact number of observations in your database? Counting manually sounds like a very very bad idea.

Fortunately, SQL has the built-in functionality of counting rows. To count the number of rows in the whole dataset use COUNT *. For example, we can count the total number of our website being visited by using the following query:


              
12

            
SELECT COUNT(*)
FROM visitors
copy

Please note, that for counting the total number of rows you must place * within parenthesis, like COUNT(*).

Opgave

Swipe to start coding

Count number of Audi cars sold from audi_cars table.

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 1. Kapitel 6
Switch to desktopSkift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder
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