Question

我正在尝试从一个表中检索post_id，post_year，post_desc，post_title，post_date，从另一个表中检索img_filename，其中post_id相等，其中is_thumb为1（其中我选择该图像作为帖子缩略图）

据我所知，没有运气：

SELECT post_id, post_year, post_desc, post_title, post_date,
FROM mjbox_posts
JOIN mjbox_images
USING (img_is_thumb)
WHERE img_is_thumb = 1
AND mjbox_images.post_id = mjbox_posts.post_id

由于

Answer 1

SELECT  p.post_id, post_year, post_desc, post_title, post_date, img_filename
FROM    mjbox_posts p
JOIN    mjbox_images i
ON      i.post_id = p.post_id
        AND i.img_is_thumb = 1

或者，如果您更喜欢USING语法，

SELECT  post_id, post_year, post_desc, post_title, post_date, img_filename
FROM    mjbox_posts p
JOIN    mjbox_images i
USING   (post_id)
WHERE   i.img_is_thumb = 1

不同之处在于第一个查询从两个表中返回post_id，您需要对其进行别名。

Answer 2

SELECT post_id, post_year, post_desc, post_title, post_date,
FROM mjbox_posts
INNER JOIN mjbox_images on mjbox_images.post_id = mjbox_posts.post_id
WHERE img_is_thumb = 1

Answer 3

SELECT post_id, post_year, post_desc, post_title, post_date, if(img_is_thumb, img_filename, null)
FROM mjbox_posts a,
mjbox_images b
WHERE a.post_id= b.post_id;

如果img_is_thumb为1，它将返回img_filename，否则它将返回null。

Mysql - 如何根据特定条件从两个表中检索字段？

3 个答案: