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SQL Joins

There are four main types of joining: Inner, Full, Left, and Right. The difference is based on which records are autocompleted with NULL if there are no matching in left or right tables.

On this example, we can see, that for INNER joining takes place only for that id's that are present in both joining columns, or for their intersection. For FULL, it makes joining for all ids that are present, or for their union. LEFT and RIGHT join does the joining for ids in the left or right table.

We can see more on the diagram:

Usually, we use INNER or LEFT join, but it depends on the situation.

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Try to join 3 tables. Select all songs and their albums and singers: join singers and songs on singer_id and songs and albums on album_id. Order albums lexicographically (column title of albums).

Use aliases for column names: song for songs.title, album for albums.title, and singer for singers.naming.

Løsning

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Sektion 2. Kapitel 2

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SQL Joins

There are four main types of joining: Inner, Full, Left, and Right. The difference is based on which records are autocompleted with NULL if there are no matching in left or right tables.

We can see more on the diagram:

Usually, we use INNER or LEFT join, but it depends on the situation.

Opgave

Swipe to start coding

Use aliases for column names: song for songs.title, album for albums.title, and singer for singers.naming.

Løsning

Skift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder

Var alt klart?

Tak for dine kommentarer!

Sektion 2. Kapitel 2

Skift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder