嵌套选择数据库sql查询

Question

how to order a values fetched from database??

SELECT * FROM comment;
------------------------------------
| commentid | content | read_unread|
------------------------------------
1              hello      Unread
2              hi         read    


Select * From replies;
//commentid Fk from table "  comment  " so it means row 1 from table comments has 2 replies
------------------------------------
| repnum | rep_content | commentid |
------------------------------------
1              see ya        1
2              ok            1

i want to show this in a table html/php like this

---

comment num |  Content | replies count
--------------------------------------------------   
 1              hello    2
 2              hi       0

//the "replies count 2" came from the table replies replied to commentid 1 from table comment

how can i show this in a single query sql order by the count of the replies count???

Answer 1

You can use JOIN on SQL query :

SELECT c.commentid, c.content, COUNT(r.replies) FROM comment c JOIN replies r ON r.commentid = c.commentID GROUP BY c.commentid, c.content;

More infos here : http://dev.mysql.com/doc/refman/5.7/en/join.html

Answer 2

Try it.

SELECT a.commentid, a.content, count(*) as replies_count
FROM comment a
LEFT JOIN replies b on a.commentid=b.commentid
GROUP BY a.commentid, a.content

Answer 3

Left join and count from replies table is your buddies. Inner join will remove comments those don't yet get any replies so here left join will be required. And count from replies is your requirement so count(*) will not work.

SELECT A.commentid AS comment_num, A.content AS Content, count(B.commentid) as replies_count
FROM comment A
LEFT JOIN replies B on A.commentid=B.commentid
GROUP BY A.commentid, A.content

Answer 4

Try this :

SELECT a.commentid, a.content, count(b.repnum) as replies_count 
FROM comment a left join replies b on a.commentid = b.commentid 
GROUP by a.commentid