MySQL如何对带有连接的查询执行COUNT（*）操作？
问题描述：
有谁知道我该如何执行COUNT（*）这样的查询？MySQL如何对带有连接的查询执行COUNT（*）操作？
SELECT reviews.review_id, reviews.reviewers_rating, reviews.reviewers_name, reviews.review_date, reviews.pros, reviews.cons, products.product_name, products.slug, products.community_rating, products.number_of_votes, products.users_rating, products.thumb_link, categories.category_name_single
FROM reviews
LEFT JOIN products ON reviews.product_id = products.product_id
LEFT JOIN categories ON products.category = categories.category_id
WHERE reviews.approved =1
ORDER BY reviews.review_date DESC
谢谢！不需要
答
试试这个：
SELECT Count(reviews.review_id), reviews.review_id, reviews.reviewers_rating, reviews.reviewers_name, reviews.review_date, reviews.pros, reviews.cons, products.product_name, products.slug, products.community_rating, products.number_of_votes, products.users_rating, products.thumb_link, categories.category_name_single
FROM reviews
LEFT JOIN products ON reviews.product_id = products.product_id
LEFT JOIN categories ON products.category = categories.category_id
WHERE reviews.approved =1
Group By reviews.review_id
ORDER BY reviews.review_date DESC
答
左连接的，一样的购买，你不必指望所有领域，一个就足够
SELECT COUNT(review_id) FROM reviews WHERE approved =1
编辑：
如果要计数的产品比你的评论应该是这样的：
SELECT products.*, count(r.review_id) AS reviews_count FROM products AS p
LEFT JOIN reviews AS r ON p.product_id = r.product_id AND r.approved=1
GROUP BY products.product_id
+0
谢谢，但这会让我所有的批准审查，对不对？我需要的是例如仅获得某个产品的所有批准评论 – CodeVirtuoso 2011-06-08 13:11:08
答
SELECT COUNT(*) FROM reviews
LEFT JOIN products ON reviews.product_id = products.product_id
LEFT JOIN categories ON products.category = categories.category_id
WHERE reviews.approved = 1 AND ...
ORDER BY reviews.review_date DESC
您试图计算哪一列？ – Bill 2011-06-08 12:55:53
review_id，但只有所有其他约束适用的评论。即我不需要评论的总数，但说只计算某个产品的评论。 – CodeVirtuoso 2011-06-08 13:09:44
检查我的更新回答 – 2011-06-08 13:42:30