I have two tables: groups
and group_members
.
The groups
table contains all the information for each group, such as its ID, title, description, etc.
In the group_members
table, it lists all the members who are apart of each group like this:
group_id | user_id
1 | 100
2 | 23
2 | 100
9 | 601
Basically, I want to list THREE groups on a page, and I only want to list groups which have MORE than four members. Inside the <?php while ?>
loop, I then want to four members who are apart of that group. I'm having no trouble listing the groups, and listing the members in another internal loop, I just cannot refine the groups so that ONLY those with more than 4 members show.
Does anybody know how to do this? I'm sure it's with MySQL joins.
MySQL use HAVING statement for this tasks.
Your query would look like this:
SELECT g.group_id, COUNT(m.member_id) AS members
FROM groups AS g
LEFT JOIN group_members AS m USING(group_id)
GROUP BY g.group_id
HAVING members > 4
example when references have different names
SELECT g.id, COUNT(m.member_id) AS members
FROM groups AS g
LEFT JOIN group_members AS m ON g.id = m.group_id
GROUP BY g.id
HAVING members > 4
Also, make sure that you set indexes inside your database schema for keys you are using in JOINS as it can affect your site performance.
SELECT DISTINCT groups.id,
(SELECT COUNT(*) FROM group_members
WHERE member_id = groups.id) AS memberCount
FROM groups
Your groups_main
table has a key column named id
. I believe you can only use the USING
syntax for the join if the groups_fans
table has a key column with the same name, which it probably does not. So instead, try this:
LEFT JOIN groups_fans AS m ON m.group_id = g.id
Or replace group_id
with whatever the appropriate column name is in the groups_fans
table.
Maybe I am off the mark here and not understanding the OP but why are you joining tables?
If you have a table with members and this table has a column named "group_id", you can just run a query on the members table to get a count of the members grouped by the group_id.
SELECT group_id, COUNT(*) as membercount
FROM members
GROUP BY group_id
HAVING membercount > 4
This should have the least overhead simply because you are avoiding a join but should still give you what you wanted.
If you want the group details and description etc, then add a join from the members table back to the groups table to retrieve the name would give you the quickest result.
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.