I am having a bit of trouble with my query.
As you can see i am running two queries. This all looks very well and mysql takes it like a man. But the result that i get is 5 times the same stuff.
SELECT s.category_id, p.product_id
FROM (
SELECT ros_categories.category_id
FROM ros_categories, ros_variantIndex
WHERE ros_categories.name = ros_variantIndex.variantText
AND ros_categories.group = 'Sizes'
LIMIT 0 , 5
) s, (
SELECT ros_product.product_id
FROM ros_product, ros_variantIndex
WHERE ros_product.vart = ros_variantIndex.vart
LIMIT 0 , 5
) p
Output:
+-------------+------------+
| category_id | product_id |
+-------------+------------+
| 110 | 1 |
| 7 | 1 |
| 8 | 1 |
| 9 | 1 |
| 10 | 1 |
| 110 | 1 |
| 7 | 1 |
| 8 | 1 |
| 9 | 1 |
| 10 | 1 |
| 110 | 1 |
| 7 | 1 |
| 8 | 1 |
| 9 | 1 |
| 10 | 1 |
| 110 | 1 |
| 7 | 1 |
| 8 | 1 |
| 9 | 1 |
| 10 | 1 |
| 110 | 1 |
| 7 | 1 |
| 8 | 1 |
| 9 | 1 |
| 10 | 1 |
+-------------+------------+
25 rows in set (0.01 sec)
What is going on here? Is this my problem or is mysql being strange?
EDIT:
Thanks for explaining me what the problem was. I fixed it using several joins. So thanks for pointing out my error and naming the problem :-) And sorry bout the silly question
What is going on here? Is this my problem or is mysql being strange?
What you've done is create a Cartesian product also known as a Cross Join. typically you just join s and p to get what you want but the JOIN criteria isn't clear.
Perhaps you want this (guessing at columns on your tables)
SELECT s.category_id, p.product_id
FROM (
SELECT ros_categories.category_id
FROM ros_categories, ros_variantIndex
WHERE ros_categories.name = ros_variantIndex.variantText
AND ros_categories.group = 'Sizes'
LIMIT 0 , 5
)s
INNER JOIN (
SELECT ros_product.product_id, ros_product.category_id
FROM ros_product, ros_variantIndex
WHERE ros_product.vart = ros_variantIndex.vart
LIMIT 0 , 5
)p
on s.category_id = p.category_id
It is just a cross product of two temporary tables representing the respective result sets of the subqueries.
Related
I have a MySQL table like this:
+------+--------+--------+
| ID | UserID | Score |
+------+--------+--------+
| 1 | 3 | 12 |
| 2 | 3 | 11 |
| 3 | 3 | 12 |
| 4 | 2 | 14 |
| 5 | 4 | 8 |
| 6 | 2 | 13 |
+------+--------+--------+
From this I want to top 3 scores from entire table and a top score from particular user
+------+--------+--------+
| ID | UserID | Score |
+------+--------+--------+
| 4 | 2 | 14 |
| 6 | 2 | 13 |
| 3 | 3 | 12 |
| 5 | 4 | 8 |
+------+--------+--------+
Is this something I can get done in a single query?
Any help is appreciated
Thanks in advance!
spoiler alert ;)
(SELECT * FROM tableA ORDER BY score DESC LIMIT 3)
UNION
(SELECT * FROM tableB WHERE UserID = 4 ORDER BY score DESC LIMIT 1);
For certain definitions of "single query", sure... If you're willing to use sub queries or a union.
The best performance will probably come from two queries, but you can join them in a UNION for convenience if you wish.
I am designing a simple architecture where i have a table which stores users and some elements that they like so my table structure is something like this:
+---------+---------+
| user_id | like_id |
+---------+---------+
| 1 | 4 |
| 2 | 2 |
| 4 | 4 |
| 4 | 3 |
| 5 | 4 |
| 6 | 7 |
| 7 | 5 |
| 34 | 6 |
| 3 | 8 |
| 2 | 3 |
| 2 | 5 |
| 1 | 3 |
| 1 | 10 |
| 1 | 12 |
| 2 | 10 |
+---------+---------+
Now what i will have is id of any user (lets say user_id = 1 ) and i want a query to get all the other users who have similar Likes as that of 1.
So in the Output for user_id = 1 will be :
+---------------------------+------------------------+----------------+
| users_with_common_likes | no_of_common_likes | common_likes |
+---------------------------+------------------------+----------------+
| 4 | 2 | 3,4 |
| 2 | 2 | 3,10 |
| 5 | 1 | 4 |
+---------------------------+------------------------+----------------+
What I have achieved :
I can do this using a sub-query as below :
SELECT user_id
FROM `user_likes`
WHERE `like_id`
IN (
SELECT GROUP_CONCAT( `like_id` )
FROM user_likes
WHERE user_id =1
)
AND user_id !=1
LIMIT 0 , 30
However this query is not giving all the users,it misses the user_id = 2 which has like id 3 in common with user_id=1.
and i cant figure out how to find the remaining 2 columns.
Also I feel that this is not the best way to to this as this table will contain thousands of data and it may effect system performance.
I would like to do this with a single Mysql Query.
This assumes a PK formed on user_id,like_id...
SELECT y.user_id
, GROUP_CONCAT(y.like_id) likes
, COUNT(*) total
FROM my_table x
JOIN my_table y
ON y.like_id = x.like_id
AND y.user_id <> x.user_id
WHERE x.user_id = 1
GROUP
BY y.user_id;
i am loosing it over the following problem:
i have a table with participants and points. each participant can have up to 11 point entries of which i only want the sum of the top 6.
in this example lets say we want the top 2 of 3
+----+---------------+--------+
| id | participantid | points |
+----+---------------+--------+
| 1 | 1 | 11 |
+----+---------------+--------+
| 2 | 3 | 1 |
+----+---------------+--------+
| 3 | 3 | 4 |
+----+---------------+--------+
| 4 | 2 | 3 |
+----+---------------+--------+
| 5 | 1 | 5 |
+----+---------------+--------+
| 6 | 2 | 10 |
+----+---------------+--------+
| 7 | 2 | 9 |
+----+---------------+--------+
| 8 | 1 | 3 |
+----+---------------+--------+
| 9 | 3 | 4 |
+----+---------------+--------+
as a result i want something like
+---------------+--------+
| participantid | points |
+---------------+--------+
| 2 | 19 |
+---------------+--------+
| 1 | 16 |
+---------------+--------+
| 3 | 8 |
+---------------+--------+
(it should be ordered DESC by the resulting points)
is this at all possible with mysql? in one query?
oh and the resulting participant ids should be resolved into the real names from another 'partcipant' table where
+----+------+
| id | name |
+----+------+
| 1 | what |
+----+------+
| 2 | ev |
+----+------+
| 3 | er |
+----+------+
but that should be doable with a join at some point... i know...
Using one of the answers from ROW_NUMBER() in MySQL for row counts, and then modifying to get the top.
SELECT ParticipantId, SUM(Points)
FROM
(
SELECT a.participantid, a.points, a.id, count(*) as row_number
FROM scores a
JOIN scores b ON a.participantid = b.participantid AND cast(concat(a.points,'.', a.id) as decimal) <= cast(concat(b.points,'.', b.id) as decimal)
GROUP BY a.participantid, a.points, a.id
) C
WHERE row_number IN (1,2)
GROUP BY ParticipantId
Had an issue with ties until I arbitrarily broke them with the id
i'm build an exercises web app and i'm working with two tables like this:
Table 1: weekly_stats
| id | code | type | date | time |
|----|--------------|--------------------|------------|----------|
| 1 | CC | 1 | 2015-02-04 | 19:15:00 |
| 2 | CC | 2 | 2015-01-28 | 19:15:00 |
| 3 | CPC | 1 | 2015-01-26 | 19:15:00 |
| 4 | CPC | 1 | 2015-01-25 | 19:15:00 |
| 5 | CP | 1 | 2015-01-24 | 19:15:00 |
| 6 | CC | 1 | 2015-01-23 | 19:15:00 |
| .. | ... | ... | ... | ... |
Table 2: global_stats
| id | exercise_number |correct | wrong |
|----|-----------------|--------|-----------|
| 1 | 138 | 1 | 0 |
| 2 | 246 | 1 | 0 |
| 3 | 988 | 1 | 10 |
| 4 | 13 | 5 | 0 |
| 5 | 5 | 4 | 7 |
| 6 | 5 | 4 | 7 |
| .. | ... | ... | ... |
What i would like is to get MAX(correct-wrong) and MIN(correct-wrong) and now i'm working with this query:
SELECT
exercise_number,
date,
time
FROM weekly_stats AS w JOIN global_stats AS g
ON w.id=g.id
WHERE correct - wrong = (SELECT MAX(correct - wrong) from global_stats)
UNION
SELECT
exercise_number,
date,
time
FROM weekly_stats AS w JOIN global_stats AS g
ON w.id=g.id
WHERE correct - wrong = (SELECT MIN(correct - wrong) from global_stats);
This query is working good, except for one thing: when "WHERE correct - wrong = (SELECT MIN(correct - wrong)[...]" selects more than one row, the row selected is the first but i would like to have returned the most recent (in other words: ordered by datetime(date, time)). Is it possible?
Thanks!
I think you can solve it like this:
SELECT * FROM (
SELECT
1 as sort_column,
exercise_number,
date,
time
FROM weekly_stats AS w JOIN global_stats AS g
ON w.id=g.id
WHERE correct - wrong = (SELECT MAX(correct - wrong) from global_stats)
ORDER BY date DESC, time DESC
LIMIT 1 ) as a
UNION
SELECT * FROM (
SELECT
2 as sort_column,
exercise_number,
date,
time
FROM weekly_stats AS w JOIN global_stats AS g
ON w.id=g.id
WHERE correct - wrong = (SELECT MIN(correct - wrong) from global_stats)
ORDER BY date DESC, time DESC
LIMIT 1) as b
ORDER BY sort_column;
Here is the documentation about how UNION works.
I have two tables, rating:
+-----------+-----------+-------------+----------+
| rating_id | entity_id | rating_code | position |
+-----------+-----------+-------------+----------+
| 1 | 1 | Quality | 0 |
| 2 | 1 | Value | 0 |
| 3 | 1 | Price | 0 |
+-----------+-----------+-------------+----------+
And rating_option
+-----------+-----------+------+-------+----------+
| option_id | rating_id | code | value | position |
+-----------+-----------+------+-------+----------+
| 1 | 1 | 1 | 1 | 1 |
| 2 | 1 | 2 | 2 | 2 |
| 3 | 1 | 3 | 3 | 3 |
| 4 | 1 | 4 | 4 | 4 |
| 5 | 1 | 5 | 5 | 5 |
| 6 | 2 | 1 | 1 | 1 |
| 7 | 2 | 2 | 2 | 2 |
| 8 | 2 | 3 | 3 | 3 |
| 9 | 2 | 4 | 4 | 4 |
| 10 | 2 | 5 | 5 | 5 |
| 11 | 3 | 1 | 1 | 1 |
| 12 | 3 | 2 | 2 | 2 |
| 13 | 3 | 3 | 3 | 3 |
| 14 | 3 | 4 | 4 | 4 |
| 15 | 3 | 5 | 5 | 5 |
+-----------+-----------+------+-------+----------+
I need a SQL query (not application level, must stay in the database) which will select a set of ratings randomly. A sample result would look like this, but would pick a random value for each rating_id on subsequent calls:
+-----------+-----------+------+-------+----------+
| option_id | rating_id | code | value | position |
+-----------+-----------+------+-------+----------+
| 1 | 1 | 1 | 1 | 1 |
| 8 | 2 | 3 | 3 | 3 |
| 15 | 3 | 5 | 5 | 5 |
+-----------+-----------+------+-------+----------+
I'm totally stuck on the random part, and grouping by rating_id has been a crap shoot so far. Any MySQL ninjas want to take a stab?
Thanks,
Joe
EDIT: I've tried rand() in a bunch of combinations, and I'm sure that it will be necessary to create the randomness of the result, but I cannot figure out how to return one random row for each of the rows in rating. I cannot use order by rand() limit 1 because I need three rows, and order by rand() limit 3 won't give me one of each rating_id, which is the ultimate goal. I need a combination of rand() and either subqueries or joins so that I can ensure one of each rating_id.
Alright, a little messy, but seems to do the job. Someone may know what they're doing better than I do that can clean this up:
SELECT random.rating_id, random.rand_option_id, r3.code, r3.value, r3.position
FROM
(SELECT r.rating_id,
(SELECT r2.option_id
FROM rating_option r2
WHERE r2.rating_id = r.rating_id
ORDER BY RAND() LIMIT 1) AS 'rand_option_id'
FROM rating_option r
GROUP BY r.rating_id
) random
LEFT JOIN rating_option AS r3 ON r3.option_id = rand_option_id
Results (varies every time, of course):
+-----------+----------------+------+-------+----------+
| rating_id | rand_option_id | code | value | position |
+-----------+----------------+------+-------+----------+
| 1 | 4 | 4 | 4 | 4 |
| 2 | 6 | 1 | 1 | 1 |
| 3 | 13 | 3 | 3 | 3 |
+-----------+----------------+------+-------+----------+
You could use the rand() function to do sorting in a select on the rating table.
For example:
select rating_id from rating order by rand() limit 1
As clarified in your comments, and the other posts above
select * from rating_option order by rand()
will return all records in a random order... However, if you want only X number, then inclue that as the limit as noted by others
select * from rating_option order by rand() limit 5 (or whatever number)
Have you looked into the rand() function?
SELECT column FROM table
ORDER BY RAND()
LIMIT 1
http://www.petefreitag.com/item/466.cfm
http://dev.mysql.com/doc/refman/5.0/en/mathematical-functions.html#function_rand
Sample code
select *
from rating_option
group by rating_id
order by rand()