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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 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
copy

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

Opgave

Swipe to start coding

Count the number of different cars models in the 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 7
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book
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
copy

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

Opgave

Swipe to start coding

Count the number of different cars models in the 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 7
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?
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