我有一个 php 文件查询 mySql 数据库,该数据库在一张表上设置了电影,在另一张表上设置了 movieRatings。我想计算某部电影的“5 星”、“4 星”等评级的数量。我的查询有效,但是它非常慢,因为我意识到对于我要查找的每部电影,它都要遍历整个 movieRatings 表 5 次。
我的查询:
$sql = "SELECT *
FROM MOVIE_INFO,
(SELECT count(ratingValue) as star5 FROM MOVIE_RATINGS2 WHERE itemID=$b[0] AND ratingValue = 5 ) SUB,
(SELECT count(ratingValue) as star4 FROM MOVIE_RATINGS2 WHERE itemID=$b[0] AND ratingValue = 4 ) SUB1,
(SELECT count(ratingValue) as star3 FROM MOVIE_RATINGS2 WHERE itemID=$b[0] AND ratingValue = 3 ) SUB2,
(SELECT count(ratingValue) as star2 FROM MOVIE_RATINGS2 WHERE itemID=$b[0] AND ratingValue = 2 ) SUB3,
(SELECT count(ratingValue) as star1 FROM MOVIE_RATINGS2 WHERE itemID=$b[0] AND ratingValue = 1 ) SUB4
WHERE movieID = $b[0]";
我想如果我可以从该特定电影的电影评级中提取一次子集,它会大大加快它的速度,但我不记得如何做到这一点。
最佳答案
您正在执行多个子选择。相反,尝试分组查询,例如
SELECT ratingValue, COUNT(ratingValue) FROM MOVIE_INFO
WHERE movieID = $b[0]
GROUP BY ratingValue
您将针对每个星级类别返回一行。第一列将是评分本身(例如 1),第二列将是具有该星数的评分数。
关于php - 对电影数据库的 PHP mySQL 查询速度极慢,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/16249414/