[英]How to count rows in one table based on another table in mysql 2
嘗試使用COUNT(c.section)
這樣當section沒有關聯時結果為null時,計數為零
SELECT d.abbreviation
, COUNT(c.section) num
FROM departments d
LEFT JOIN courses c ON c.section LIKE CONCAT(d.abbreviation, "%")
GROUP BY d.abbreviation
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