Easiest explained through an example.
A father has children who win races.
How many of a fathers offspring have won a race and how many races in total have a fathers offspring won. (winners and wins)
I can easily figure out the total amount of wins but sometimes a child wins more than one race so to figure out winners I need only sum if the child has won, not all the times it has won.
In the below extract from a query I cannot use Distinct, so this doesn't work
SUM(CASE WHEN r.finish = '1' AND DISTINCT h.runnersid THEN 1 ELSE 0 END ) AS winners,
This also won't work
SUM(SELECT DISTINCT r.runnersid FROM runs r WHERE r.finish='1') AS winners
This works when I need to find the total amount of wins.
SUM(CASE WHEN r.finish = '1' THEN 1 ELSE 0 END ) AS wins,
Here is a sqlfiddle http://sqlfiddle.com/#!2/e9a81/1
Let's take this step by step.
You have two pieces of information you are looking for: Who has won a race, and how many races have they one.
Taking the first one, you can select a distinct runnersid where they have a first place finish:
SELECT DISTINCT runnersid
FROM runs
WHERE finish = 1;
For the second one, you can select every runnersid where they have a first place finish, count the number of rows returned, and group by runnersid to get the total wins for each:
SELECT runnersid, COUNT(*) AS numWins
FROM runs
WHERE finish = 1
GROUP BY runnersid;
The second one actually has everything you want. You don't need to do anything with that first query, but I used it to help demonstrate the thought process I take when trying to accomplish a task like this.
Here is the SQL Fiddle example.
EDIT
As you've seen, you don't really need the SUM here. Because finish represents a place in the race, you don't want to SUM that value, but you want to COUNT the number of wins.
EDIT2
An additional edit based on OPs requirements. The above does not match what OP needs, but I left this in as a reference to any future readers. What OP really needs, as I understand it now, is the number of children each father has that has run a race. I will again explain my thought process step by step.
First I wrote a simple query that pulls all of the winning father-son pairs. I was able to use GROUP BY to get the distinct winning pairs:
SELECT father, name
FROM runs
WHERE finish = 1
GROUP BY father, name;
Once I had done that, I used it is a subquery and the COUNT(*) function to get the number of winners for each father (this means I have to group by father):
SELECT father, COUNT(*) AS numWinningChildren
FROM(SELECT father, name
FROM runs
WHERE finish = 1
GROUP BY father, name) t
GROUP BY father;
If you just need the fathers with winning children, you are done. If you want to see all fathers, I would write one query to select all fathers, join it with our result set above, and replace any values where numWinningChildren is null, with 0.
I'll leave that part to you to challenge yourself a bit. Also because SQL Fiddle is down at the moment and I can't test what I was thinking, but I was able to test those above with success.
I think you want the father name along with the count of the wins by his sons.
select father, count(distinct(id)) wins
from runs where father = 'jack' and finish = 1
group by father
sqlfiddle
I am not sure if this is what you are looking for
Select user_id, sum(case when finish='1' then 1 else 0 end) as total
From table
Group by user_id
Related
I have a table (tblExam) showing exam data score designed as follow:
Exam Name: String
Score: number(pecent)
Basically I am trying to pull the records by Exam name where the score are less than a specific amount (0.695 in my case).
I am using the following statement to get the results:
SELECT DISTINCTROW tblExam.name, Count(tblExam.name) AS CountOfName
FROM tblExam WHERE (((tblExam.Score)<0.695))
GROUP BY tblExam.name;
This works fine but does not display the exam that have 0 records more than 0.695; in other words I am getting this:
Exam Name count
firstExam 2
secondExam 1
thirdExam 3
The count of 0 and any exams with score above 0.695 do not show up. What I would like is something like this:
Exam Name count
firstExam 2
secondExam 1
thirdExam 3
fourthExam 0
fifthExam 0
sixthExam 2
.
..
.etc...
I hope that I am making sense here. I think that I need somekind of LEFT JOIN to display all of the exam name but I can not come up with the proper syntax.
It seems you want to display all name groups and, within each group, the count of Score < 0.695. So I think you should move < 0.695 from the WHERE to the Count() expression --- actually remove the WHERE clause.
SELECT
e.name,
Count(IIf(e.Score < 0.695, 1, Null)) AS CountOfName
FROM tblExam AS e
GROUP BY e.name;
That works because Count() counts only non-Null values. You could use Sum() instead of Count() if that seems clearer:
Sum(IIf(e.Score < 0.695, 1, 0)) AS CountOfName
Note DISTINCTROW is not useful in a GROUP BY query, because the grouping makes the rows unique without it. So I removed DISTINCTROW from the query.
Do I detect a contradiction? The query calls for results <0.695 but your text says you are also looking for results >0.695. Perhaps I don't understand. Does this give you what you are looking for:
SELECT DISTINCTROW tblExam.ExamName, Count(tblExam.ExamName) AS CountOfExamName
FROM tblExam
WHERE (((tblExam.Score)<0.695 Or (tblExam.Score)>0.695))
GROUP BY tblExam.ExamName;
I have a table for a game where more people play the game it will repeat each other.. I can remove duplicates no problem but this one is different because I want to remove the others while keeping the highest score is it possible to do it?
for example
Name Level Score
Green 99 797,000
Green 99 819,000
Green 99 970,000
Green 99 890,000
I want to keep row 3 and remove the others.
In the example you show, you can get the top row this way:
SELECT * FROM `thistable` ORDER BY score DESC LIMIT 1
But I assume you have more than one Name in the table. If you want the highest score for a specific name:
SELECT * FROM `thistable` WHERE Name = 'Green' ORDER BY Score DESC LIMIT 1
If you want results for multiple names, but the row with the highest score for each one, it's a bit more complex:
SELECT * FROM `thistable`
JOIN (SELECT Name, MAX(Score) AS Score FROM `thistable` GROUP BY Name) AS x
USING (Name, Score);
This type of problem is commonly tagged greatest-n-per-group and it's a frequent question.
PS: Don't take the downvotes seriously. Stack Overflow has become a pretty nasty place. There will always be someone who thinks you didn't ask a valid question, or didn't ask it "correctly."
I'm working on a sports database, and I want to write a query that will return the name and the statistical value for certain categories. For example, goal leader, assist leader, points leader, +/- leader, penalty minutes leader, etc. I am using a table called NJDSkaters which contains player names and stats from a specific team. Here is the query code:
SELECT CONCAT(PlayerName,' - ',Goals) AS GoalLeader, CONCAT(PlayerName,' - ',Assists)
CONCAT(PlayerName,' - ',Points) AS PointsLeader
FROM NJDSkaters
WHERE Goals = (SELECT DISTINCT MAX(Goals) FROM NJDSkaters)
OR Assists = (SELECT DISTINCT MAX(Assists) FROM NJDSkaters)
OR Points = (SELECT DISTINCT MAX(Points) FROM NJDSkaters);
Here is a snippet from my skater register table which will show the players who should be returned by this query:
As you can see, my desired return query should have 'Ilya Kovalchuk - 37' returned as GoalLeader, 'Patrik Elias - 52' as AssistLeader, and 'Ilya Kovalchuk - 83' as PointsLeader. Running the query does provide these results, but there is extra information included that I do not want, as you can see here:
My question is, how do i get rid of the excess information? I only want the leaders in each category, and I don't want to see the #2 player listed, even if that player is #1 in some other category. Essentially, what I'm saying, is I want only 1 row in this table. Before, I had code that would return all players with the leaders at the top, so this code is a step closer to my desired result, but now I'm stuck. Searching for an answer to this problem has been challenging, as finding a way to ask it generally is difficult.
You need to PIVOT your data, I would use something like this:
SELECT
MAX(CASE WHEN NJDSkaters.Goals=mx.goals
THEN CONCAT(PlayerName,' - ', NJDSkaters.Goals) END) GoalLeader,
MAX(CASE WHEN NJDSkaters.Assists=mx.assists
THEN CONCAT(PlayerName,' - ', NJDSkaters.Assists) END) AssistsLeader,
MAX(CASE WHEN NJDSkaters.Points=mx.points
THEN CONCAT(PlayerName,' - ', NJDSkaters.Points) END) PointsLeader
FROM
NJDSkaters INNER JOIN (
SELECT MAX(Goals) goals, MAX(Assists) assists, MAX(Points) points
FROM NJDSkaters) mx
ON NJDSkaters.Goals=mx.goals
OR NJDSkaters.Assists=mx.assists
OR NJDSkaters.Points=mx.points
Please see fiddle here.
You might also want to use GROUP_CONCAT instead of MAX in case that more than one player shares the same maximum value:
SELECT
CONCAT(GROUP_CONCAT(CASE WHEN NJDSkaters.Goals=mx.goals
THEN PlayerName END), ' - ', mx.goals) GoalLeader,
CONCAT(GROUP_CONCAT(CASE WHEN NJDSkaters.Assists=mx.assists
THEN PlayerName END), ' - ', mx.assists) AssistsLeader,
CONCAT(GROUP_CONCAT(CASE WHEN NJDSkaters.Points=mx.points
THEN PlayerName END), ' - ', mx.points) PointsLeader
FROM
NJDSkaters INNER JOIN (
SELECT MAX(Goals) goals, MAX(Assists) assists, MAX(Points) points
FROM NJDSkaters) mx
ON NJDSkaters.Goals=mx.goals
OR NJDSkaters.Assists=mx.assists
OR NJDSkaters.Points=mx.points
A little explanation:
The subquery mx will return the maximum number of goals, the maximum number of assists, and the maximum points
I'm joining the table NJDSkaters with this subquery to return all of the rows that have the maximum number of goals OR the maximum number of assists OR the maximum points
CASE WHEN NJDSkaters.Goals=mx.goals THEN PlayerName END will return the PlayerName if that player has the maximum number of goals, otherwise it will return NULL. The same goes for assists and points.
using GROUP_CONCAT I'm concatenating all of the players names returned by the CASE WHEN. GROUP_CONCAT will skip NULL values and will only concatenate players that have the maximum value for their category
using CONCAT I'm concatenating the string returned by the GROUP_CONCAT above with the maximum value for each category.
why not to limit the result by using LIMIT 1?
Although several . questions . come . close . to what I want (and as I write this stackoverflow has suggested several more, none of which quite capture my problem), I just don't seem to be able to find my way out of the SQL thicket.
I have a single table (let's call it the user_classification_fct) that has three fields: user, week, and class (e.g. user #1 in week #1 had a class of 'Regular User', while user #2 in week #1 has a class of 'Infrequent User'). (As an aside, I have implemented classes as INTs, but wanted to work with something legible in the form of VARCHAR while I sorted out the SQL.)
What I want to do is produce a summary report of how user behaviour is changing in aggregate along the lines of:
There were 50 users who were regular users in both week 1 and week 2 and ...
There were 10 users who were regular users in week 1, but fell to infrequent users in week 2
There were 5 users who went from infrequent in week 1 to regular in week 2
... and so on ...
What makes this slightly more tricky is that user #5000 might only have started using the service in week 2 and so have no record in the table for week 1. In that case, I'd want to see a NULL FOR week 1 and a 'Regular User' (or whatever is appropriate) for week 2. The size of the table is not strictly relevant, but with 5 weeks' worth of data I'm looking at 42 million rows, so I do not want to insert 4 'fake' rows of 'Non-User' for someone who only starts using the service in week 5 or something.
To me this seems rather obviously like a case for using a LEFT or RIGHT JOIN in MySQL because the NULL should come through on the 'missing' record.
I have tried using both WHERE and AND conditions on the LEFT JOINs and am just not getting the 'right' answers (i.e. I either get no NULL values at all in the case of trailing WHERE conditions, or my counts are far, far too high for the number of distinct users (which is ca. 10 million) in the case of the AND constraints used below). Here's was my last attempt to get this working:
SELECT
ucf1.class_nm AS 'Class in 2012/15',
ucf2.class_nm AS 'Class in 2012/16',
ucf3.class_nm AS 'Class in 2012/17',
ucf4.class_nm AS 'Class in 2012/18',
ucf5.class_nm AS 'Class in 2012/19',
count(*) AS 'Count'
FROM
user_classification_fct ucf5
LEFT JOIN user_classification_fct ucf4
ON ucf5.user_id=ucf4.user_id
AND ucf5.week_key=201219 AND ucf4.week_key=201218
LEFT JOIN user_classification_fct ucf3
ON ucf4.user_id=ucf3.user_id
AND ucf4.week_key=201218 AND ucf3.week_key=201217
LEFT JOIN user_classification_fct ucf2
ON ucf3.user_id=ucf2.user_id
AND ucf3.week_key=201217 AND ucf2.week_key=201216
LEFT JOIN user_classification_fct ucf1
ON ucf2.user_id=ucf1.user_id
AND ucf2.week_key=201216 AND ucf1.week_key=201215
GROUP BY 1,2,3,4,5;
In looking at the various other questions on stackoverflow.com, it may well be that I need to perform the queries one-at-a-time and UNION the result sets together or use parentheses to chain them one-to-another, but those approaches are not ones that I'm familiar with (yet) and I can't even get a single LEFT JOIN (i.e. week 5 to week 1, dropping all the other weeks of data) to return something useful.
Any tips would be much, much appreciated and I would really appreciate suggestions that work in MySQL as switching database products is not an option.
You can do this with a group by. I would start by summarizing all the possible combinations for the five weeks as:
select c_201215, c_201216, c_201217, c_201218, c_201219,
count(*) as cnt
from (select user_id,
max(case when week_key=201215 then class_nm end) as c_201215,
max(case when week_key=201216 then class_nm end) as c_201216,
max(case when week_key=201217 then class_nm end) as c_201217,
max(case when week_key=201218 then class_nm end) as c_201218,
max(case when week_key=201219 then class_nm end) as c_201219
from user_classification_fct ucf
group by user_id
) t
group by c_201215, c_201216, c_201217, c_201218, c_201219
This may solve your problem. If you have 5 classes (including NULL), then this will return at most 5^5 or 3,125 rows.
This fits into Excel, so you can do the final processing there. Alternatively, you can still use the database.
If you want to extract pairs of weeks, then I would suggest putting the above into a temporary table, say "t". And doing a series of extracts with unions:
select *
from ((select '201215' as weekstart, c_201215, c_201216, sum(cnt) as cnt
from t
group by c_201215, c_201216
) union all
(select '201216', c_201216, c_201217, sum(cnt) as cnt
from t
group by c_201216, c_201217
) union all
(select '201217', c_201217, c_201218, sum(cnt) as cnt
from t
group by c_201217, c_201218
) union all
(select '201218', c_201218, c_201219, sum(cnt) as cnt
from t
group by c_201218, c_201219
)
) tg
order by 1, cnt desc
I suggest putting it in a subquery because you don't want to message around with common-subquery optimizations on such a large table. You'll get to your final answer by summarizing first, and then bringing the data together.
I'm stumped with how to do the following purely in MySQL, and I've resorted to taking my result set and manipulating it in ruby afterwards, which doesn't seem ideal.
Here's the question. With a dataset of 'items' like:
id state_id price issue_date listed
1 5 450 2011 1
1 5 455 2011 1
1 5 490 2011 1
1 5 510 2012 0
1 5 525 2012 1
...
I'm trying to get something like:
SELECT * FROM items
WHERE ([some conditions], e.g. issue_date >= 2011 and listed=1)
AND state_id = 5
GROUP BY id
HAVING AVG(price) <= 500
ORDER BY price DESC
LIMIT 25
Essentially I want to grab a "group" of items whose average price fall under a certain threshold. I know that my above example "group by" and "having" are not correct since it's just going to give the AVG(price) of that one item, which doesn't really make sense. I'm just trying to illustrate my desired result.
The important thing here is I want all of the individual items in my result set, I don't just want to see one row with the average price, total, etc.
Currently I'm just doing the above query without the HAVING AVG(price) and adding up the individual items one-by-one (in ruby) until I reach the desired average. It would be really great if I could figure out how to do this in SQL. Using subqueries or something clever like joining the table onto itself are certainly acceptable solutions if they work well! Thanks!
UPDATE: In response to Tudor's answer below, here are some clarifications. There is always going to be a target quantity in addition to the target average. And we would always sort the results by price low to high, and by date.
So if we did have 10 items that were all priced at $5 and we wanted to find 5 items with an average < $6, we'd simply return the first 5 items. We wouldn't return the first one only, and we wouldn't return the first 3 grouped with the last 2. That's essentially how my code in ruby is working right now.
I would do almost an inverse of what Jasper provided... Start your query with your criteria to explicitly limit the few items that MAY qualify instead of getting all items and running a sub-select on each entry. Could pose as a larger performance hit... could be wrong, but here's my offering..
select
i2.*
from
( SELECT i.id
FROM items i
WHERE
i.issue_date > 2011
AND i.listed = 1
AND i.state_id = 5
GROUP BY
i.id
HAVING
AVG( i.price) <= 500 ) PreQualify
JOIN items i2
on PreQualify.id = i2.id
AND i2.issue_date > 2011
AND i2.listed = 1
AND i2.state_id = 5
order by
i2.price desc
limit
25
Not sure of the order by, especially if you wanted grouping by item... In addition, I would ensure an index on (state_id, Listed, id, issue_date)
CLARIFICATION per comments
I think I AM correct on it. Don't confuse "HAVING" clause with "WHERE". WHERE says DO or DONT include based on certain conditions. HAVING means after all the where clauses and grouping is done, the result set will "POTENTIALLY" accept the answer. THEN the HAVING is checked, and if IT STILL qualifies, includes in the result set, otherwise throws it out. Try the following from the INNER query alone... Do once WITHOUT the HAVING clause, then again WITH the HAVING clause...
SELECT i.id, avg( i.price )
FROM items i
WHERE i.issue_date > 2011
AND i.listed = 1
AND i.state_id = 5
GROUP BY
i.id
HAVING
AVG( i.price) <= 500
As you get more into writing queries, try the parts individually to see what you are getting vs what you are thinking... You'll find how / why certain things work. In addition, you are now talking in your updated question about getting multiple IDs and prices at apparent low and high range... yet you are also applying a limit. If you had 20 items, and each had 10 qualifying records, your limit of 25 would show all of the first item and 5 into the second... which is NOT what I think you want... you may want 25 of each qualified "id". That would wrap this query into yet another level...
What MySQL does makes perfectly sense. What you want to do does not make sense:
if you have let's say 4 items, each with price of 5 and you put HAVING AVERAGE <= 7 what you say is that the query should return ALL the permutations, like:
{1} - since item with id 1, can be a group by itself
{1,2}
{1,3}
{1,4}
{1,2,3}
{1,2,4}
...
and so on?
Your algorithm of computing the average in ruby is also not valid, if you have items with values 5, 1, 7, 10 - and seek for an average value of less than 7, element with value 10 can be returned just in a group with element of value 1. But, by your algorithm (if I understood correctly), element with value 1 is returned in the first group.
Update
What you want is something like the Knapsack problem and your approach is using some kind of Greedy Algorithm to solve it. I don't think there are straight, easy and correct ways to implement that in SQL.
After a google search, I found this article which tries to solve the knapsack problem with AI written in SQL.
By considering your item price as a weight, having the number of items and the desired average, you could compute the maximum value that can be entered in the 'knapsack' by multiplying desired_cost with number_of_items
I'm not entirely sure from your question, but I think this is a solution to your problem:
SELECT * FROM items
WHERE (some "conditions", e.g. issue_date > 2011 and listed=1)
AND state_id = 5
AND id IN (SELECT id
FROM items
GROUP BY id
HAVING AVG(price) <= 500)
ORDER BY price DESC
LIMIT 25
note: This is off the top of my head and I haven't done complex SQL in a while, so it might be wrong. I think this or something like it should work, though.