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SQL Inner Join

JOIN operator makes combining the records into two tables based on the related column between them. For example, we want to join singers and songs columns in some way. These tables have the same column: singer_id in songs and id in singers. We join them by this column, and now records are rearranged into groups by this id.

JOIN can be applied for multiple tables, and the syntax is:


              12345678
            
--do not run this query
SELECT columns
FROM table1 INNER JOIN table2
ON table1.col1 = table2.col2
WHERE conditions
GROUP BY columns
HAVING agg_condition
ORDER BY columns

JOIN is an alternative to nested queries. Let's look at the following example, find all songs released between 1970 and 1990:


              123
            
SELECT songs.title
FROM albums INNER JOIN songs ON songs.album_id = albums.id
WHERE year>=1970 AND year<=1990

This diagram shows how INNER JOIN works. Chosen columns albums_id and id are joined, and only ids present in both columns appear in the result query. Intersection of sets (1, 2, 3) and (1, 2, 4, 2) is a (1, 2, 2).

This way, we avoid using nested queries. Using Joins is a common practice, and in the next chapters, we'll learn other types, except INNER JOIN.

Uppgift

Swipe to start coding

Write the query to find all songs created by AC/DC. Print song's title (title) and singer (naming) to the console.

Lösning

Byt till skrivbordet för praktisk övningFortsätt där du är med ett av alternativen nedan

Var allt tydligt?

Tack för dina kommentarer!

Avsnitt 2. Kapitel 1

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SQL Inner Join

JOIN can be applied for multiple tables, and the syntax is:


              12345678
            
--do not run this query
SELECT columns
FROM table1 INNER JOIN table2
ON table1.col1 = table2.col2
WHERE conditions
GROUP BY columns
HAVING agg_condition
ORDER BY columns

JOIN is an alternative to nested queries. Let's look at the following example, find all songs released between 1970 and 1990:


              123
            
SELECT songs.title
FROM albums INNER JOIN songs ON songs.album_id = albums.id
WHERE year>=1970 AND year<=1990

This way, we avoid using nested queries. Using Joins is a common practice, and in the next chapters, we'll learn other types, except INNER JOIN.

Uppgift

Swipe to start coding

Write the query to find all songs created by AC/DC. Print song's title (title) and singer (naming) to the console.

Lösning

Byt till skrivbordet för praktisk övningFortsätt där du är med ett av alternativen nedan

Var allt tydligt?

Tack för dina kommentarer!

Avsnitt 2. Kapitel 1

Byt till skrivbordet för praktisk övningFortsätt där du är med ett av alternativen nedan