MYSQL顯示不計數

Question

我在MySQL中有兩個表格：曲目和評分。我希望查詢算多少收視每個磁道有，這就是爲什麼我使用以下命令：

SELECT t.*, COUNT(*) as ratings 
FROM tracks t, ratings r 
WHERE t.trackID = r.trackID 
GROUP BY t.trackID 
ORDER BY ratings DESC 

那麼我現在的問題是，當一個音軌沒有評級，但（這樣算爲0 ）它不會顯示，但我也希望它顯示何時還沒有任何評級。我希望有一個人可以幫助我。提前致謝！史蒂芬。

Answer 1

試試這個，希望你會發現它有幫助。

SELECT t.*, (select count(*) from ratings r where r.trackID = t.trackID) as ratingsCount from tracks t order by ratingsCount DESC; 

Answer 2

您必須使用LEFT JOIN來保留所有左側（即軌道）記錄。

SELECT t.*, COUNT(*) as ratings 
FROM tracks t 
    LEFT JOIN ratings r 
ON t.trackID = r.trackID 
GROUP BY t.trackID 
ORDER BY ratings DESC