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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
Multiple filtering on one column

What if we are interested only in two models: let it be A4 and A5?

Of course, we could write WHERE model = 'A4' OR model = 'A5'. But is there a point in writing two conditions for the same column? This problem is also solved in SQL by using IN statement. To check if a value from a column is one of acceptable use WHERE column IN ('value1', 'value2', ...) syntax. For example,


              
123

            
SELECT *
FROM audi_cars
WHERE model IN ('A4', 'A5')
copy

WHERE column IN ('value1', 'value2') is equvivalent to WHERE column = 'value1' OR column = 'value2'. It also works for numeric values.

Opgave

Swipe to start coding

From audi_cars extract cars with engine size (enginesize column) 1.5 and 2.9 using IN statement.

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 2. Kapitel 5
toggle bottom row

book
Multiple filtering on one column

What if we are interested only in two models: let it be A4 and A5?

Of course, we could write WHERE model = 'A4' OR model = 'A5'. But is there a point in writing two conditions for the same column? This problem is also solved in SQL by using IN statement. To check if a value from a column is one of acceptable use WHERE column IN ('value1', 'value2', ...) syntax. For example,


              
123

            
SELECT *
FROM audi_cars
WHERE model IN ('A4', 'A5')
copy

WHERE column IN ('value1', 'value2') is equvivalent to WHERE column = 'value1' OR column = 'value2'. It also works for numeric values.

Opgave

Swipe to start coding

From audi_cars extract cars with engine size (enginesize column) 1.5 and 2.9 using IN statement.

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 2. Kapitel 5
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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