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Data Manipulation using SQL
Data Manipulation using SQL
SQL Left & Right Join
LEFT JOIN returns all records from the left table and matching records from the right table. For records with no matching, it completes the fields with NULL. For example, let's select all albums joined with songs ids with LEFT JOIN:
SELECT albums.title, songs.id FROM albums LEFT JOIN songs ON songs.album_id = albums.id
On the diagram for this query, we can see that not all albums have songs in a table, so absent fields are autocompleted with NULL. Similarly, we can see in the result query: some albums have empty id's for the songs, because there are no songs for these albums.
Swipe to start coding
Do the joining for tables albums and songs using INNER JOIN, RIGHT JOIN, FULL JOIN, and check the difference. Then, find the number of songs for each album (even if there are no songs in it). Think about which JOIN you can use here. Order everything by albums title.
Solution
Passez à un bureau pour une pratique réelleContinuez d'où vous êtes en utilisant l'une des options ci-dessousMerci pour vos commentaires !
SQL Left & Right Join
LEFT JOIN returns all records from the left table and matching records from the right table. For records with no matching, it completes the fields with NULL. For example, let's select all albums joined with songs ids with LEFT JOIN:
SELECT albums.title, songs.id FROM albums LEFT JOIN songs ON songs.album_id = albums.id
On the diagram for this query, we can see that not all albums have songs in a table, so absent fields are autocompleted with NULL. Similarly, we can see in the result query: some albums have empty id's for the songs, because there are no songs for these albums.
Swipe to start coding
Do the joining for tables albums and songs using INNER JOIN, RIGHT JOIN, FULL JOIN, and check the difference. Then, find the number of songs for each album (even if there are no songs in it). Think about which JOIN you can use here. Order everything by albums title.
Solution
Passez à un bureau pour une pratique réelleContinuez d'où vous êtes en utilisant l'une des options ci-dessousMerci pour vos commentaires !
Passez à un bureau pour une pratique réelleContinuez d'où vous êtes en utilisant l'une des options ci-dessous