使用phpmyadmin在mysql中进行交叉表查询

Question

I have 2 tables in mysql, tbl_post & tbl_comment,

I require a crosstab query , based upon tbl_post.post_id , the result should be like

all elments of tbl_post + count of records form tbl_comment, where 
tbl_post.post_id == tbl_comment.post_id

eg Result should be like ::

post_id,title,content,tags,status,create_time,update_time,author_id,likes + count from tbl_comment

Please see the image.

I am new to sql just having academic knowledge , and couldn't figure it out. Any help is appreciated.

Answer 1

I think you just need to join tbl_post to a subquery which counts the number of comments for each post.

SELECT t1.*,
       COALESCE(t2.post_count, 0) AS post_count
FROM tbl_post t1
LEFT JOIN
(
    SELECT post_id, COUNT(*) AS post_count
    FROM tbl_comment
    GROUP BY post_id
) t2
    ON t1.post_id = t2.post_id

If you want to create a view using the above query then you need to get a bit creative. The following attempt will fail because the above query has a subquery in it:

CREATE VIEW PostCountView AS
SELECT t1.*,
       COALESCE(t2.post_count, 0) AS post_count
FROM tbl_post t1
...

Instead, you can create a view for the subquery, and then use that in a second view for the main query:

CREATE VIEW PostCountView AS
SELECT post_id, COUNT(*) AS post_count
FROM tbl_comment
GROUP BY post_id

CREATE VIEW PostCountMainView AS
SELECT t1.*,
       COALESCE(t2.post_count, 0) AS post_count
FROM tbl_post t1
LEFT JOIN PostCountView t2
    ON t1.post_id = t2.post_id

Answer 2

select t1.post_id,
       t1.title,
       t1.content,
       t1.tags,
       t1.status,
       t1.create_time,
       t1.updated_time,
       t1.author_id,
       t1.likes,
       count(t2.post_id)
from tbl_post t1
LEFT JOIN tbl_comment t2
    on t1.post_id = t2.post_id
group by t1.post_id;