即使返回的连接结果为空，mysqli_num_rows也会返回1

Question

这是我的疑问：

$query = 'SELECT b.author as author, b.review as review FROM location_final_similar a LEFT JOIN location_reviews b ON (a.uuid = b.uuid AND a.originalLocationID = b.originalLocationID) WHERE a.finalLocationID = "'.$locationID.'"';

正如您在上面所看到的，我唯一关心的是获取作者和评论（从表location_reviews中检索）。

当我使用$ locationID测试其中包含location_reviews内的数据时，mysqli_num_rows将返回正确的计数。

但是当我使用$ locationID测试时，location_reviews中没有数据，mysqli_num_rows仍然会返回1，但是作者和＆amp;审查null。那我怎么能避免这个呢？如果没有给定ID的评论，我需要mysqli_num_rows返回0。

Answer 1

您必须使用INNER JOIN（或者RIGHT JOIN），例如

SELECT b.author as author, b.review as review FROM location_final_similar a INNER JOIN location_reviews b ON (a.uuid = b.uuid AND a.originalLocationID = b.originalLocationID) WHERE a.finalLocationID = 1

请参阅Difference between INNER and OUTER joins以获得更好的解释。