I have two tables - results and contestants. Result table cointains
result_id (PK)
resul_contestant (who scored this)
value (how much did he scored)
result_discipline(where he scored this)
contestants table cointains
contestant_id (PK)
contestant_name
contestant_category
What I want to do is to select results for all contestants, but I only want to show one result per contestant - the highest (lowest) one.
So far I managed to do this:
SELECT * FROM contenstants
JOIN results ON result_contestant = contenstant_id
WHERE result_discipline = 1 AND contestant_category = 1
ORDER BY value DESC
GROUP BY contenstant_id;
However, this gives me syntax error. If I delete the GROUP BY line, I got results ordered from highest, but if any of the contestants scored in this discipline more than once, I got all of his scores.
If I delete the ORDER BY line, I got only one result per contestant, but it returns the first record in db, not the highest one.
How to fix this command to be valid? Also, there are some less_is_better disciplines, where I want the lowest score, but as far as I could use the ORDER BY on final query, it should be achieved by replacing DESC with ASC.
Thanks.
Don't use group by. Using select * with group by just doesn't make sense. Instead, use a filter to get the row you want:
SELECT *
FROM contenstants c JOIN
results r
ON r.result_contestant = c.contestant_id
WHERE r.result_discipline = 1 AND c.contestant_category = 1 AND
r.value = (select min(r2.value)
from results r2
where r2.result_contestant = r.result_contestant and
r2.result_discipline = r.result_discipline
)
ORDER BY value DESC;
Note: I'm not sure if you want min() or max() in the subquery.
Related
In this database:
I need to write an SQL query that will display the name of each client of the agent with the highest agent rating in the company.
What I'm trying right now is,
SELECT ClientName
FROM CLIENT.ClientName
WHERE CLIENT.AgentID = AGENT.AgentID AND MAX(AGENT.AgentRating);
I'm new to MySQL, so I just want to check if I'm using the MAX and AND operators properly, or if there's a simpler way to do this.
Try using a subquery to select the highest rated agent, then join it to your CLIENT table to select the names of the associated clients. Something like this:
SELECT ClientName
FROM CLIENT.ClientName
JOIN (
SELECT AgentID FROM AGENT ORDER BY AgentRating DESC LIMIT 1
) sq ON sq.AgentID = CLIENT.AgentID
The subquery (SELECT AgentID FROM AGENT ORDER BY AgentRating DESC LIMIT 1) sq selects the AgentID column from the AGENT table
Then with ORDER BY AgentRating DESC it orders that column by the AgentRating descending placing the highest rating at the top of the results.
Then the LIMIT 1 limits the rows returned to 1, giving you only 1 (the first returned) record from the AGENT table that we just ordered to put the highest rated agent at the top.
Then when you JOIN that result from the subquery with your CLIENT table on the AgentID, you will only get results in your CLIENT table maching the selected AgentID from the subquery.
Basically, I have two separate queries, which I need to somehow merge into one set of results.
![This is Table 1, which shows the sum of each group's salary]
1
Here is the queries I wrote to form the tables.
SELECT con_stagename, SUM(p_daily_salary) AS sum_salary
FROM CONTENDER, PARTICIPANT
WHERE p_contender = con_id
GROUP BY con_id;
SELECT MAX(sum_salary) AS max_salary
FROM (SELECT con_stagename, SUM(p_daily_salary) AS sum_salary
FROM CONTENDER, PARTICIPANT
WHERE p_contender = con_id
GROUP BY con_id) T2;
And the question is, if I want the result to be a single row of values, which the name of the group with the highest salary, and the actual amount. How would I do it? I've been trying to use JOIN operations but there was not luck.
SELECT con_stagename, SUM(p_daily_salary) AS sum_salary
FROM CONTENDER, PARTICIPANT
WHERE p_contender = con_id
GROUP BY con_id
ORDER BY 2 DESC
LIMIT 1
I try to select in a one to many relation childs where records of childs is 1. For fetching childs with one record I use the following query.
Here is the simple query which works if I do not use wherestatement
select a.iid,
account_id,
count(*) as props
from accounts_prop a
group by a.account_id
having props = 1
when I use where I get back totally other result. In this case I get records which shows that props are having 1 record but actually having more than one
select a.iid,
account_id,
count(*) as props
from accounts_prop a
where a.von >= '2017-08-25'
group by a.account_id
having props = 1
What I'm missing in this case
the where condition filter you original rows so
where a.von >= '2017-08-25'
reduce the number of rows involved in query
the having clause work on the result of a query so in you have filter with a where (or not ) you obtain different result
In your case in the first query your count is calculate on all the rows in your in the second query your count is calculated only on a subset
This can explain why you obtain different resul from the two query
Upon closer inspection, your original query is not even determinate:
SELECT
a.iid, -- OK, but which value of iid do we choose?
a.account_id,
COUNT(*) AS props
FROM accounts_prop a
GROUP BY a.account_id
HAVING props = 1
The query makes no sense because you are selecting the iid column while aggregating on other columns. Which value of iid should be chosen for each account? This is not clear, and your query would not even run on certain versions of MySQL or most other databases.
Instead, put your logic to find accounts with only a single record into a subquery, and then join to that subquery to get the full records for each match:
SELECT a1.*
FROM accounts_prop a1
INNER JOIN
(
SELECT account_id
FROM accounts_prop
GROUP BY account_id
HAVING COUNT(*) = 1
) a2
ON a1.account_id = a2.account_id
WHERE a1.von >= '2017-08-25'
I'm running two queries.
The first one gets unique IDs. This executes in ~350ms.
select parent_id
from duns_match_sealed_air_072815
group by duns_number
Then I paste those IDs into this second query. With >10k ids pasted in, it also executes in about ~350ms.
select term, count(*) as count
from companies, business_types, business_types_to_companies
where
business_types.id = business_types_to_companies.term_id
and companies.id = business_types_to_companies.company_id
and raw_score > 25
and diversity = 1
and company_id in (paste,ten,thousand,ids,here)
group by term
order by count desc;
When I combine these queries into one it takes a long time to execute. I don't know how long because I stopped it after minutes.
select term, count(*) as count
from companies, business_types, business_types_to_companies
where
business_types.id = business_types_to_companies.term_id
and companies.id = business_types_to_companies.company_id
and raw_score > 25
and diversity = 1
and company_id in (
select parent_id
from duns_match_sealed_air_072815
group by duns_number
)
group by term
order by count desc;
What is going on?
It's down to the way it processes the query - I believe it has to run your embedded query once for each row, whereas using two queries allows you to store the result.
Hope this helps!
The query has been re-written using JOIN, but particularly I've used EXISTS instead of IN. This is a short in the dark. It is possible that there may be many values generated in the sub-query causing the outer query to struggle while it goes through matching each item returned from the sub-query.
select term, count(*) as count
from companies c
inner join business_types_to_companies bc on bc.company_id = c.id
inner join business_types b on b.id = bc.term_id
where
raw_score > 25
and diversity = 1
and exists (
select 1
from duns_match_sealed_air_072815
where parent_id = c.id
)
group by term
order by count desc;
First, with respect, your subquery doesn't use GROUP BY in a sensible way.
select parent_id /* wrong GROUP BY */
from duns_match_sealed_air_072815
group by duns_number
In fact, it misuses the pernicious MySQL extension to GROUP BY. Read this. http://dev.mysql.com/doc/refman/5.6/en/group-by-handling.html . I can't tell what your application logic intends from this query, but I can tell you that it actually returns an unpredictably selected parent_id value associated with each distinct duns_number value.
Do you want
select MIN(parent_id) parent_id
from duns_match_sealed_air_072815
group by duns_number
or something like that? That one selects the lowest parent ID associated with each given number.
Sometimes MySQL has a hard time optimizing the WHERE .... IN () query pattern. Try a join instead. Like this:
select term, count(*) as count
from companies
join (
select MIN(parent_id) parent_id
from duns_match_sealed_air_072815
group by duns_number
) idlist ON companies.id = idlist.parent_id
join business_types_to_companies ON companies.id = business_types_to_companies.company_id
join business_types ON business_types.id = business_types_to_companies.term_id
where raw_score > 25
and diversity = 1
group by term
order by count desc
To optimize this further we'll need to see the table definitions and the output from EXPLAIN.
I'm trying to compare two set of resutls aving hard time to undesrtand how subqueries work and if they are efficient. I'm not gonna explain all my tables, but just think i have apair of arrays...i might do it in php but i wonder if i can do it in mysql right away...
this is my query to check how many items user 1 has in lists he owns
SELECT DISTINCT *
FROM list_tb
INNER JOIN item_to_list_tb
ON list_tb.list_id = item_to_list_tb.list_id
WHERE list_tb.user_id = 1
ORDER BY item_to_list_tb.item_id DESC
this is my query to check how many items user 2 has in lists he owns
SELECT DISTINCT *
FROM list_tb
INNER JOIN item_to_list_tb
ON list_tb.list_id = item_to_list_tb.list_id
WHERE list_tb.user_id = 1
ORDER BY item_to_list_tb.item_id DESC
now the problem is that i would intersect those results to check how many item_id they have in common...
thanks!!!
Unfortunately, MySQL does not support the Intersect predicate. However, one way to accomplish that goal would be to exclude List_Tb.UserId from your Select and Group By and then count by distinct User_Id:
Select ... -- everything except List_Tb.UserId
From List_Tb
Inner Join Item_To_List_Tb
On List_Tb.List_Id = Item_To_List_Tb.List_Id
Where List_Tb.User_Id In(1,2)
Group By ... -- everything except List_Tb.UserId
Having Count( Distinct List_Tb.User_Id ) = 2
Order By item_to_list_tb.item_id Desc
Obviously you would replace the ellipses with the actual columns you want to return and on which you wish to group.