即使返回的连接结果为空，mysqli_num_rows也会返回1

Question

这是我的查询:

$query = 'SELECT b.author as author, b.review as review FROM location_final_similar a LEFT JOIN location_reviews b ON (a.uuid = b.uuid AND a.originalLocationID = b.originalLocationID) WHERE a.finalLocationID = "'.$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 location_reviews 中包含数据的 $locationID 进行测试时，mysqli_num_rows 将返回正确的计数。

但是当我使用 location_reviews 中没有数据的 $locationID 进行测试时，mysqli_num_rows 仍将返回 1，但作者和评论为空。那么我怎样才能避免这种情况呢？如果给定 ID 没有评论，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

参见Difference between INNER and OUTER joins以获得一个很好的解释。