I'm trying to select results from two different unrelated tables, showcase and questions to appear in a feed. They should be ordered by the common column hotness which is a float value.
SELECT s.id,s.date,s.title,s.views,s.image,s.hidpi,s.width,s.description,u.display_name,u.avatar
FROM showcase AS s
INNER JOIN users AS u ON s.user_id = u.id
UNION
SELECT q.id,q.date,q.title,q.views,q.text,u.display_name,u.avatar,0,0,0
FROM questions AS q
INNER JOIN users AS u ON q.user_id = u.id
ORDER BY hotness DESC
LIMIT 10
I've tried UNION, but I have no idea how I should be using it here and get this error unknown column hotness
You need to select the value in order for the ORDER BY to recognize it:
SELECT s.id,s.date,s.title,s.views,s.image,s.hidpi,s.width,s.description,u.display_name,u.avatar, s.hotness
FROM showcase AS s
INNER JOIN users AS u ON s.user_id = u.id
UNION ALL
SELECT q.id,q.date,q.title,q.views,q.text,u.display_name,u.avatar,0,0,0, q.hotness
FROM questions AS q
INNER JOIN users AS u ON q.user_id = u.id
ORDER BY hotness DESC;
Note that I also changed the UNION to UNION ALL. Unless you intend to remove duplicates, there is no reason to incur the extra processing for doing that.
You can try this query:
SELECT r.* FROM (
SELECT s.id,s.date,s.title,s.views,s.image,s.hidpi,s.width,s.description,u.display_name,u.avatar, s.hotness
FROM showcase AS s
INNER JOIN users AS u ON s.user_id = u.id
UNION
SELECT q.id,q.date,q.title,q.views,q.text,u.display_name,u.avatar,0,0,0, q.hotness
FROM questions AS q
INNER JOIN users AS u ON q.user_id = u.id
) as r
ORDER BY r.hotness DESC
LIMIT 10
You need to merge Union result in subquery to apply Order by on the result. I also added hotness in select clause, please check I take field from good table.
Related
My goal is: display how often is specific ID repeated as the topic_poster in one table, phpbb_topics, but only if the proper forum_id condition is also met, then also display the corresponding username from another table, phpbb_users.
I have successfully extracted the count of how often is one specific userID occuring as the topic_poster in table phpbb_topics, like that:
SELECT topic_poster, COUNT(topic_poster)
FROM phpbb_topics WHERE forum_id = 156
GROUP BY topic_poster
Thanks to another question on StackOverflow I now also know how to get data from another table to get the username corresponding to the specific userID, like that:
SELECT t.topic_poster, u.user_id, u.username
FROM phpbb_topics t
LEFT JOIN phpbb_users u ON u.user_id = t.topic_poster
I also managed to finally mix the two to get what I want:
SELECT t.topic_poster, COUNT(t.topic_poster), u.user_id, u.username
FROM phpbb_topics t
LEFT JOIN phpbb_users u ON u.user_id = t.topic_poster WHERE t.forum_id = 156
GROUP BY t.topic_poster
However, I do not know how to properly sort in descending or ascending order based on the counter. phpmyAdmin won't let me just click on the column's name to sort by it, and any queries i write with GROUP BY or ORDER BY are reporting errors.
Update:
after putting this in:
SELECT t.topic_poster, COUNT(t.topic_poster), u.user_id, u.username
FROM phpbb_topics t
LEFT JOIN phpbb_users u ON u.user_id = t.topic_poster WHERE t.forum_id = 156
ORDER BY COUNT(topic_poster)
the results display only one row:
topic_poster |COUNT(t.topic_poster) | user_id | username
6 | 254 6 | Opix
Same happens if I use this:
SELECT t.topic_poster, COUNT(t.topic_poster), u.user_id, u.username
FROM phpbb_topics t
LEFT JOIN phpbb_users u ON u.user_id = t.topic_poster WHERE t.forum_id = 156
ORDER BY COUNT(t.topic_poster)
Same happens if I use this:
SELECT t.topic_poster, COUNT(t.topic_poster), u.user_id, u.username
FROM phpbb_topics t
LEFT JOIN phpbb_users u ON u.user_id = t.topic_poster WHERE t.forum_id = 156
ORDER BY topic_poster
If I use this: SELECT t.topic_poster, COUNT(t.topic_poster), u.user_id, u.username FROM phpbb_topics t LEFT JOIN phpbb_users u ON u.user_id = t.topic_poster WHERE t.forum_id = 156 GROUP BY t.topic_poster I get all the results, but I can't sort by the counter.
mySQL extends the group by so you don't have to have one. However, it assumes all values for each column are the same; so it's free to pick what to put in from each column. However, if the values are different, what it picks (1 value) isn't representative of the entire set, so you must use group by when the values are different.
Put a different way: if t.forum_ID = 156 limited to a specific topic_poster, user_Id and username. you'd have no problem. But since t.forum_ID represents many different values in each of those columns, group by is needed or the engine will "somewhat" randomly select a value for each of them. The engine assumes all are the same.
Thus the downfall of the mySQL Group by extension. But, if all the non-aggregrated columns did have the same value... you get a performance gain by allowing the engine to just aggregate and 'pick' a value for each column.
Based on your response, you think you should be getting multiple rows. So that tells me the non-aggregated fields are different so add a group by...
SELECT t.topic_poster, COUNT(t.topic_poster), u.user_id, u.username
FROM phpbb_topics t
LEFT JOIN phpbb_users u ON u.user_id = t.topic_poster
WHERE t.forum_id = 156
GROUP BY t.topic_poster, u.user_id, u.username
ORDER BY COUNT(t.topic_poster)
You could have ties, so you may also want to order by poster or user name after the count...
I have the following SQL query which returns 2 results which are the same only different by a where clause.
I would like to have them combined and group them under the user names. At the moment the two results are displayed but the results are not fully combined and the users are shown twice because of the two select statements.
How can I combine the two to create a single result.
The SQL query is as follows
SELECT
COUNT (asings.user_id),
post_status.status_id as status_id,
users.name,
users.id as user_id
from asigns
LEFT JOIN
post_status on asigns.post_id = post_status.post_id
RIGHT JOIN
users on asigns.user_id = users.id
WHERE
post_status.status_id = 2
GROUP BY users.id
UNION
SELECT
COUNT(asigns.user_id),
post_status.status_id as status_id,
users.name,
users.id from asigns
LEFT JOIN
post_status on asigns.post_id = post_status.post_id
RIGHT JOIN
users on asigns.user_id = users.id
WHERE
post_status.status_id = 3
GROUP BY users.id
See in this photo the usernames are appearing twice, what I want is to join the two username, and move count as two different columns depending on the status_id
How can I solve this. Thanks
You should use a single query with conditional aggregation:
SELECT
SUM(ps.status_id = 2) AS cnt_2,
SUM(ps.status_id = 3) AS cnt_3,
u.name,
u.id as user_id
FROM users u
LEFT JOIN assigns a ON a.user_id = u.id
LEFT JOIN post_status ps ON a.post_id = ps.post_id
GROUP BY u.id;
Use SELECT distinct for the union:
SELECT distinct * FROM ([FIRST SELECT] UNION [SECOND SELECT])
Or GROUP BY username
SELECT * FROM ([FIRST SELECT] UNION [SECOND SELECT]) GROUP BY username
BUT I suggest to review your both selects, if it differs just in the where clause so use where clause with the operator OR and you handle it just by one SELECT
Although your are using a LEFT and a RIGHT join and implicitly an INNER join between users and asigns, the WHERE clause transforms all the joins to INNER joins, because you are picking only the matching rows from post_status.
So, you only need INNER joins and conditional aggregation:
SELECT COALESCE(SUM(ps.status_id = 2), 0) counter_2,
COALESCE(SUM(ps.status_id = 3), 0) counter_3,
u.name,
u.id AS user_id
FROM users u
INNER JOIN asigns a ON a.user_id = u.id
INNER JOIN post_status ps ON ps.post_id = a.post_id
WHERE ps.status_id IN (2, 3)
GROUP BY u.id;
I have a query
select c.CommentId
,c.CommentText
, c.CommenterId
, c.CommentDate
, u.first_name
, u.last_name
, i.ImageName
, i.Format
from comment c
join users u
on c.CommenterId = u.user_id
join user_profile_image i
on u.user_id = i.UserId
where PostId = 76
order
by CommentDate desc
limit 10
This query returns empty results when i.ImageName field is empty in the table. I want to return the row if the ImageName field is emty. How should I do this?
JOIN defaults to INNER JOIN for MySQL - try changing
join user_profile_image i
to
LEFT join user_profile_image i
The accepted answer here has a good visual explanation: Difference in MySQL JOIN vs LEFT JOIN
To include the rows when the ImageName field is empty, use LEFT JOIN, like this:
SELECT c.CommentId,c.CommentText, c.CommenterId, c.CommentDate, u.first_name,
u.last_name,i.ImageName,i.Format
FROM comment c
INNER JOIN users u ON c.CommenterId=u.user_id
LEFT JOIN user_profile_image i ON u.user_id=i.UserId
WHERE PostId = 76
ORDER BY CommentDate DESC
LIMIT 10;
The issue isn't exactly that i.ImageName is empty. The issue is that there is no image associated with the user. The join doesn't find an image, and without a match, the user isn't returned.
The solution is to use left join. My inclination is to write the query entirely with left join:
select c.CommentId, c.CommentText, c.CommenterId, c.CommentDate,
u.first_name, u.last_name,
i.ImageName, i.Format
from comment c left join
users u
on c.CommenterId = u.user_id left join
user_profile_image i
on u.user_id = i.UserId
where PostId = 76
order by c.CommentDate desc
limit 10;
Note: This assumes that PostId is in the comment table, which seems reasonable given the table names.
I built working MySQL query:
SELECT
v.*, u.username
FROM
video AS v, users AS u
WHERE
v.type = 'public'
AND
v.user_ID = u.user_ID
Now I want to add a third table and count() results from the table comments where video_ID from this table will be equal to those from the table video.
I tried this but it wasn't successful:
SELECT
v.*, u.username, count(c.video_ID)
FROM
video AS v, users AS u, comments AS c
WHERE
v.type = 'public'
AND
v.user_ID = u.user_ID
AND
v.video_ID = c.video_ID
In return I want to get the number of comments related to certain video_ID's.
I don't understand how to make it work correctly in one query.
Could you please help me out?
Thank you in advance,
Ilia
If you are using an aggregate function like a COUNT in a query, you need to specify the grouping with a GROUP BY clause.
Try this
SELECT
v.*,
u.username,
count(c.video_ID) AS comment_count
FROM
video AS v
INNER JOIN users AS u ON v.user_ID = u.user_ID
INNER JOIN comments AS c ON v.video_ID = c.video_ID
WHERE
v.type = 'public'
GROUP BY
v.id,
u.username,
v.v.add_time
ORDER BY
v.add_time
While MySQL lets you leave out the some elements of the GROUP BY clause, it is good practice to specify them.
When joining two tables, it is good practice to use the INNER JOIN syntax, rather than a WHERE filter.
I've looked around for an answer to this but I'm not finding it. I have a site with articles stored in an article table and writers in the user table. I wanted to get a list of authors ordered by how recently they'd written an article.
This gives me the User ids:
SELECT distinct a.user_id
FROM `article` as a
ORDER BY a.id desc
The problem is that as soon as I try to bring the names in by joining the order changes so that it's by user id. I've tried this:
SELECT distinct a.user_id, u.name
FROM `article` as a
LEFT JOIN user as u on u.id = a.user_id
ORDER BY a.id desc, u.id desc
and
SELECT distinct a.user_id, u.name
FROM `article` as a
LEFT JOIN user as u on u.id = a.user_id
ORDER BY u.id desc, a.id desc
but both alter the order of the names. I'm obviously doing something stupid, but what?
The fact that DISTINCT happens to work with ORDER BY in your first example is a fluke, and not standard SQL. You need something like this:
SELECT a.user_id, u.name
FROM article a
LEFT JOIN user u ON u.id = a.user_id
GROUP BY a.user_id
ORDER BY MAX(a.id) desc
try this
SELECT a.user_id, u.name
FROM `article` a
LEFT JOIN user u on u.id = a.user_id
GROUP BY a.user_id
ORDER BY a.id desc
Your ORDER BY sorts the rows by either the User ID and/or Article ID (depending on the example).
If you want reliable sorting by name, then include the u.name field in the ORDER BY fields.
this is postgres syntax, but you can easily translate it into mysql
select u.*, q.last_article_id
from user u
inner join (
select a.user_id, max(a.id) as last_article_id
from article a
group by a.user_id
) q
on u.id = a.q.id
order by q.last_article_id desc
Something along the lines of the following should work:
select users.id, articles.id, max(articles.created_at) as recent_date
from users
left join articles on users.id = articles.user_id
group by articles.id
order by recent_date
Not sure what exactly your fields are named and all, but this should point you in the right direction.
You got a lot of answers to choose from... I believe the key to what you're asking is use of the aggregate function MAX() http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_max