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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
Tables aliases

As for columns, you can also assign some alias to the table name. It is very useful when you work with multiple tables at once, as they may have identical names.

To assign an alias to a table name use the same syntax as for columns. For example,


              
12

            
SELECT column1, column2
FROM table_name AS t
copy

With this technique, you can refer to certain columns by using alias.column. It also works for the whole table name. For example,


              
12

            
SELECT t.column1, t.column2
FROM table_name AS t
copy

and


              
12

            
SELECT table_name.column1, table_name.column2
FROM table_name
copy

queries will return the same result. It's all about usability.

Opgave

Swipe to start coding

Extract columns model, price, fueltype, and mpg from audi_cars table. Use a alias for the table and extract columns using this alias. Print first 10 rows.

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 9
toggle bottom row

book
Tables aliases

As for columns, you can also assign some alias to the table name. It is very useful when you work with multiple tables at once, as they may have identical names.

To assign an alias to a table name use the same syntax as for columns. For example,


              
12

            
SELECT column1, column2
FROM table_name AS t
copy

With this technique, you can refer to certain columns by using alias.column. It also works for the whole table name. For example,


              
12

            
SELECT t.column1, t.column2
FROM table_name AS t
copy

and


              
12

            
SELECT table_name.column1, table_name.column2
FROM table_name
copy

queries will return the same result. It's all about usability.

Opgave

Swipe to start coding

Extract columns model, price, fueltype, and mpg from audi_cars table. Use a alias for the table and extract columns using this alias. Print first 10 rows.

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 9
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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