我有两个表，我想为每个帖子显示一张照片，但是当运行查询为每张照片显示帖子时
照片表:
+------------------------------------------------------------+
| photo_id | post_id | photo_name |
+------------------------------------------------------------+
| 1 | 1 | flower.jpg |
+------------------------------------------------------------+
| 2 | 1 | book.jpg |
+------------------------------------------------------------+
| 3 | 2 | pen.jpg |
+------------------------------------------------------------+
| 4 | 3 | man.jpg |
+------------------------------------------------------------+
| 5 | 3 | women.jpg |
+------------------------------------------------------------+
| 6 | 3 | boy.jpg |
+------------------------------------------------------------+
张贴表:
+--------------------------------+
| post_id | post_title |
+--------------------------------+
| 1 | flower |
+--------------------------------+
| 2 | book |
+--------------------------------+
| 3 | pen |
+--------------------------------+
| 4 | man |
+--------------------------------+
| 5 | women |
+--------------------------------+
| 6 | boy |
+--------------------------------+
使用流动的 SQL 查询和 INNER JOIN 但我的结果显示如下:
SELECT
Photo.photo_name,
Post.post_title
FROM Photo
INNER JOIN Post
ON Photo.post_id = Post.post_id
ORDER BY Post.post_id
执行后查询结果:
+-----------------------------+
| post_title | photo_name |
+-----------------------------+
| flower | flower.jpg |
+-----------------------------+
| flower | flower.jpg |
+-----------------------------+
| book | book.jpg |
+-----------------------------+
| book | book.jpg |
+-----------------------------+
| pen | pen.jpg |
+-----------------------------+
| pen | pen.jpg |
+-----------------------------+
| man | man.jpg |
+-----------------------------+
| man | man.jpg |
+-----------------------------+
| women | women.jpg |
+-----------------------------+
| women | women.jpg |
+-----------------------------+
| boy | boy.jpg |
+-----------------------------+
| boy | boy.jpg |
+-----------------------------+
我在帖子表中有 6 个帖子，我想为每个帖子获取一张照片，但我的结果按照片数显示帖子
最佳答案
您可以使用分组方式。由于您还没有定义，在帖子有多张照片的情况下使用哪张照片，我们可以获得帖子的 Max() 照片:
SELECT
MAX(Photo.photo_name),
Post.post_title
FROM Photo
INNER JOIN Post
ON Photo.post_id = Post.post_id
GROUP BY Post.post_id, Post.post_title
ORDER BY Post.post_id
关于mysql - 如何在MySQL中通过查询从每个帖子的照片表中选择一张照片，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/52759348/