I have a download-component and want the categories to display the subcats and item count in advance. 1 of both works, but when trying to get both, the result is the multiply of both.
The code I use:
SELECT a.*,
count(b.parentid) AS catscount,
count(c.id) AS itemscount
FROM (jos_foc_downl_categories AS a LEFT JOIN jos_foc_downl_items AS c ON c.catid = a.id )
LEFT JOIN jos_foc_downl_categories AS b ON b.parentid = a.id
WHERE a.parentid=0
GROUP BY a.id
This results for a category with 4 subcategories and 5 files in the number 20 for catscount and 20 for itemscount.
What's wrong with this? Thanks!
You're counting all rows, including duplicated values. Use DISTINCT to only count each distinct value once:
SELECT a.*,
count(DISTINCT b.parentid) AS catscount,
count(DISTINCT c.id) AS itemscount
....
Related
I want to get the total likes and total count of the every post in a single query with the help of joins.
I am using this query. but the result is wrong
SELECT blog.id, count(blog_comments.id) as likes , count(blog_likes.id) as comments
FROM blog LEFT JOIN
blog_comments
ON blog.id = blog_comments.blog_id LEFT JOIN
blog_likes
ON blog.id = blog_likes.blog_id
GROUP BY blog.id
Please check the image for table structure:
Your problem is that you are aggregating along two dimensions at the same time. The produces a Cartesian product -- a row with each like pairs with each comment, for a total of l * c rows.
The simplest way to fix this is to use the DISTINCT keyword:
SELECT b.id, count(DISTINCT bl.id) as likes , count(DISTINCT bc.id) as comments
FROM blog b LEFT JOIN
blog_comments bc
ON b.id = bc.blog_id LEFT JOIN
blog_likes
ON b.id = bl.blog_id
GROUP BY b.id;
If you have posts that have lots of likes and lots of comments, this is not recommended, because it creates a Cartesian product of the two.
There are several solutions for this, but I would recommend correlated subqueries:
select b.id,
(select count(*) from blog_likes bl where bl.blog_id = b.id) as likes,
(select count(*) from blog_comments bc where bc.blog_id = b.id) as comments
from blogs b;
This can take advantage of indexes on blog_likes(blog_id) and blog_comments(blog_id).
This is according to my table it will help you...
SELECT people.pe_name, COUNT(distinct orders.ord_id) AS num_orders, COUNT(items.item_id) AS num_items FROM people INNER JOIN orders ON orders.pe_id = people.pe_id INNER JOIN items ON items.ord_id = orders.ord_id GROUP BY people.pe_id;
I want to group order's count to show how many clients have that number of orders.
I have come up with:
select count(*) as quantidade_pedidos, clientes.id
from pedidos
inner join clientes
on pedidos.cliente_id = clientes.id
where pedidos.aprovado = 1
group by quantidade_pedidos
but I just can't group by 'quantidade_pedidos' anyway.
Is there any way to group by a temporary column? Another way of doing this? show how many clients (number) have that number of orders placed?
Example
8 orders placed -> 3 clients have 8 orders placed
etc
Your original query is wrong. You need to group by clientes.id:
select count(*) as quantidade_pedidos, c.id
from pedidos p inner join
clientes c
on p.cliente_id = c.id
where p.aprovado = 1
group by c.id;
In an aggregation query, the unaggregated columns go in the group by, not the aggregated ones.
Also note that table aliases make the query easier to write and to read.
As for the question in the first line, use a subquery:
select quantidade_pedidos, count(*)
from (select count(*) as quantidade_pedidos, c.id
from pedidos p inner join
clientes c
on p.cliente_id = c.id
where p.aprovado = 1
group by c.id
) x
group by quantidade_pedidos;
But given that the query in the question doesn't work, I'm not sure this is what you really want to do.
I've got query like:
SELECT
b.title,
b.url,
b.`date`,
b.gallery,
count(c.id) as comments_count,
a.name,
b.content,
b.comments,
LEFT(b.content, LOCATE('<page>', b.content)-1) as content_short
FROM blog b
LEFT JOIN blog_comments c ON
(b.id = c.note AND c.approved = 1)
LEFT JOIN administrators a ON
(b.aid = a.id)
WHERE
b.`date` < now() AND
b.active = 1
ORDER BY b.`date` DESC;
Now, when I remove count(c.id) as comments_count,, I've got 2 rows returned. When it's present, there's only 1 row returned.
Is there some way to fix ot or I simply have to change
count(c.id) as comments_count, to (select count(id) ascomments_countfrom blog_comments where note = b.id) as comments_count,?
Count(*) is an aggregated function, so it will apply in a group.
That means that when you count on groups, it will apply the function on every group.
The groups are formed when you use Group By, in this case, you're not using, so MySQL consider that ALL select (your joins) is ONLY 1 GROUP.
So, applies the count on the unique group and returning the count of rows.
you should add a Group by by the field you want
An example is here
I have this php/sql Query:
$result = mysql_query("
SELECT r.item_id, AVG(rating) AS avgrating, count(rating) AS count, i.item, c.category
FROM ratings AS r
LEFT JOIN items AS i
ON r.item_id = i.items_id
INNER JOIN master_cat c
ON c.cat_id = i.cat_id
GROUP BY item_id
ORDER BY avgrating DESC
LIMIT 25;");
When I output this, count is correct, it shows how much votes certain items have received.
I simply want to add a WHERE count >= 10 clause but everything breaks. Obviously, when there are thousands of items, some will get one vote and have 100%. But that is not a good indicator. I want to print out items that have at least 10 votes (or count >= 10)
You should to use having instead where
SELECT
r.item_id, AVG(rating) AS avgrating,
count(rating) AS count, i.item, c.category
FROM
ratings AS r
LEFT JOIN items AS i
ON r.item_id = i.items_id
INNER JOIN master_cat c
ON c.cat_id = i.cat_id
GROUP BY
item_id
HAVING
count >= 10
ORDER BY
avgrating DESC
LIMIT 25;
You can't use a where filter on the results of an aggregate function (count()). where is applied at the row-level, as the DB is deciding whether to include the row or not in the result set - at this point the results of the count aren't available yet.
What you want is a having clause, which is applied as one of the last steps before results are sent to the client, after all the aggregate results have been calculated.
...
GROUP BY item_id
HAVING count > 10
ORDER BY ...
you need to tell it what you want to count
having count(*) > 10
I have a query which pulls out all articles and their categories (that matches the current category).
I want it to fetch only 5 articles per category. how can i do it?
the query:
SELECT a.* FROM
Articles a
LEFT JOIN Articles_category b
ON a.id=b.article_id
LEFT JOIN Categories c
ON c.id = b.category_id
LEFT JOIN Articles_category ac1
ON ac1.main = 1 AND a.id = ac1.article_id AND ac1.position > 0
WHERE c.id = '14'
ORDER BY b.main DESC
I want it to select only 5 articles tops for each category.
You can't do it with that query. You would have to loop a similar query to that, based on the category id. You could do it in a stored procedure, or loop the query repeatedly in code.