Say I have the following tables,
lesson
id description
-----------------
1 science
2 english
3 maths
lesson_student_rel
lesson_id student_id
----------------------
1 1
1 2
1 3
2 1
3 1
3 3
lesson_tutor_rel
lesson_id tutor_id
--------------------
1 1
2 1
2 2
lesson_assistant_rel
lesson_id assistant_id
------------------------
1 1
1 2
3 2
I would like to count the total number of students, tutors and assistants for each lesson so I get a result like,
lesson_id student_count tutor_count assistant_count
---------------------------------------------------------
1 3 1 2
2 1 2 0
3 2 0 1
I think I've been looking at this too long now and have got completely stuck, I've found a few similar questions but nothing that seems to answer this. Is it possible to do with one query? Any pointers would be good - an answer would be amazing.
Thanks!
I think this does it for you:
SELECT l.id,COUNT(DISTINCT lsr.student_id) student_count,COUNT(DISTINCT ltr.tutor_id) tutor_count
,COUNT(DISTINCT lar.assistant_id) assistant_count
FROM lesson l
LEFT JOIN lesson_student_rel lsr ON lsr.lesson_id=l.id
LEFT JOIN lesson_tutor_rel ltr ON ltr.lesson_id=l.id
LEFT JOIN lesson_assistant_rel lar ON lar.lesson_id=l.id
GROUP BY l.id
Related
I want to have a SQL result look like this (match result query):
ID Arena Winner Loser Winner_score Loser_score
-----------------------------------------------------------------
1 1 Johnny Mark 16 8
2 2 Andrew Luke 16 7
Here are my tables (simplified)
Player_tbl
ID Player
-------------
1 Johnny
2 Mark
3 Andrew
4 Luke
Match_tbl
ID Match Arena
----------------------
1 Match 1 1
2 Match 2 2
Match_results_tbl
ID Match player_id player_score
-----------------------------------------
1 Match 1 1 16
2 Match 1 2 8
1 Match 2 3 16
2 Match 2 4 7
I am wondering how to structure my query to have the desired result.
Ok, I figured out my own issue. 1st, the match_results must be put in a table with a different structure, and 2nd, the inner sql query needed to be adjusted to pull from the proper database tables.
Whats the best way to check if different groups of rows in a table with the same GroupID such as different teams have a SINGLE captain? Captain Identifier for example could be '10', so its crucial that it goes through multiple records with the same groupID and checks to see if theres ONLY ONE record with the positionID as '10'. I need it to do it for all teams, i.e all groupID's
-------------------------------------------------
ID | Group ID | Name | Position|
-------------------------------------------------
1 1 John 3
2 1 jim 3
3 1 Hahn 4
4 1 Mary 4
5 1 Moe 4
6 1 Charlie 10
7 2 taylor 4
8 2 Geoff 4
9 2 adam 4
10 2 cam 10
11 3 sharon 2
12 3 tony 4
13 3 steve 3
14 3 eve 4
15 3 gwen 10
--------------------------------
So what I need it to do is check that every groupID only had ONE 10 as the position.
Thanks in advance guys. Check out the image link at the bottom.
im using mysql btw
Sorry if this is badly described
If I understood you - I think you need something like :
select groupId, sum(case when positionID='10' then 1 else 0 end) as captains
from tbl_name
group by groupID
having captains = 1
am I close???
If I understood you correctly, you want an indication that will tell you whether the groupID had more then one captain.
So what you need is this:
select groupID,case when cnt = 1 then 1 else 0 end as IND_ONE_CAPTAIN from (
select groupID, sum(case when positionid = '10' then 1 else 0 end) as cnt
from players
group by groupID)
Now IND_ONE_CAPTAIN columns consist 1 or 0, 1 is for the group id only had 1 captain, and 0 is when they had more.
I'm stuck with the following problem.
I have a website with for example supermarket shopping items. People can search the website for items.
Now I want on the search result page at the top 2 items to be displayed that I have selected to be on offer. There can be lots more items on offer.
So for example, someone would search for shampoo, the query would display all the shampoo items in the database table but I want just 2 shampoo offer items at the top of the query. There could be 2 or more shampoo offers in the database table, then the other would just not be shown.
Example with names :
Table:
id name C D
----------------------------------
1 Jack 1 1
2 Joe 1 1
3 Dave 3 0
4 Sue 1 0
5 Mike 1 1
6 Steve 4 0
7 David 1 0
8 Susan 4 1
9 Marc 1 1
10 Ronald 4 1
11 Michael 4 1
EXAMPLE 1
Query :
WHERE C = 1 AND D = 1 (But only maximum of 2 'D' records, these 2 'D' records show at the top of the result)
Desired Query Result :
id name C D
----------------------------------
1 Jack 1 1
2 Joe 1 1
4 Sue 1 0
7 David 1 0
EXAMPLE 2
Query :
WHERE C = 4 AND D = 1 (But only maximum of 2 'D' records, these 2 'D' records show at the top of the result)
Desired Query Result :
id name C D
----------------------------------
8 Susan 4 1
10 Ronald 4 1
6 Steve 4 0
I hope this explains my goal what I'm trying to achieve.
Many thanks for any help or suggestions!
That's two queries that you can combine with UNION ALL:
select * from mytable where c = 1 and d = 1 limit 2
union all
select * from mytable where c = 1 and d = 0
order by d desc;
UPDATE: If you want to have the two rows chosen randomly, then order by RAND(). (Without an ORDER BY the rows are chosen arbitrarily, which means it's not guaranteed to get the same two rows picked again when re-running the query ‐ but it's quite likely.) As we need an ORDER BY for a partial query (the first query in the complete union-alled query), we must use parentheses, because otherwise only one ORDER BY would be allowed, namely for the complete query at the query's end.
(select * from mytable where c = 1 and d = 1 order by rand() limit 2)
union all
(select * from mytable where c = 1 and d = 0)
order by d desc;
SQL fiddle: http://sqlfiddle.com/#!9/ed53f6/3.
I have this table:
ID STUDENT CLASS QUESTION ANSWER TIME
1 1 1 1 c 12:30
2 1 1 1 d 12:36
3 1 1 2 a 12:38
4 2 1 1 b 11:24
5 2 1 1 c 11:26
6 2 1 3 d 11:35
7 2 3 3 b 11:24
I'm trying to write a query that does this:
For each STUDENT in a specific CLASS select the most recent ANSWER for each QUESTION.
So, choosing class "1" would return:
ID STUDENT CLASS QUESTION ANSWER TIME
2 1 1 1 d 12:36
3 1 1 2 a 12:38
5 2 1 1 c 11:26
6 2 1 3 d 11:35
I've tried various combinations of subqueries, joins, and grouping, but nothing is working. Any ideas?
You can use a sub-query to get most recent ANSWER per QUESTION, Then use this as a derived table and join back to the original table:
SELECT m.*
FROM mytable AS m
INNER JOIN (
SELECT STUDENT, QUESTION, MAX(`TIME`) AS mTime
FROM mytable
WHERE CLASS = 1
GROUP BY STUDENT, QUESTION
) AS d ON m.STUDENT = d.STUDENT AND m.QUESTION = d.QUESTION AND m.`TIME` = d.mTime
WHERE m.CLASS = 1
Demo here
I have 3 mysql tables:
Client_courses
Client_courses_id Client_id Course_id
1 1 2
2 1 3
3 2 1
Client
Client_id Name
1 Tom
2 John
Courses
Course_id Name Price
1 Microsofr 100
2 Programming 250
3 Leadership 300
I need to calculate how much every client spent money on courses. For example: Tom spent 550 (250+300), John spent 100. And I am confused how to do it.
SELECT SUM(c.Price), cl.Name
FROM Client cl
INNER JOIN Client_courses clc ON cl.Client_id=clc.Client_id
INNER JOIN Courses cs ON clc.Course_id=cs.Course_id
GROUP BY cl.Name