SQL 외래키별 건수 얻기

1 개요

SQL 외래키별 건수 얻기

sql

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SELECT books.*, COUNT(orders.book_id) AS number_of_orders
FROM books
LEFT JOIN orders ON (books.id = orders.book_id)
GROUP BY books.id

2 같이 보기

• 외래키
• 왼쪽 조인
• GROUP BY
• COUNT()

3 참고

• https://stackoverflow.com/questions/7424913/how-to-count-the-number-of-instances-of-each-foreign-key-id-in-a-table