I have an SQL problem in regards to selecting a max value in a table/query. I am trying to return the maximum value returned from an aggregate expression as well as the associated primary key of the tuple.
I am able to return 1 tuple displaying only the maximum value when I only include the aggregate function in the select statement but I am unable to return just 1 tuple with BOTH the primary key and the max value of the aggregate expression.
Here is an example of my query:
SELECT id, MAX(SQRT((POWER((x-(-28)),2) + POWER((y-(151)),2)))) as distance
FROM table
GROUP BY id;
As you would expect this returns all the id's and the associated value from the function. It doesn't return just 1 tuple with the maximum value and the associated id.
What can I do to fix this?
One way to do this is by ordering by your expression in descending order, and only selecting the first row:
select id, distance
from (select id, SQRT((POWER((x-(-28)),2) + POWER((y-(151)),2))) as distance
from table
order by distance desc)
where rownum < 2
Starting with Oracle 12c, you can also take advantage of the fetch first n rows syntax to accomplish the same thing:
select id, SQRT((POWER((x-(-28)),2) + POWER((y-(151)),2))) as distance
from table
order by distance desc
fetch first row only
If more than one row shares the same maximum distance value, you can also conveniently adjust the syntax to support ties:
select id, SQRT((POWER((x-(-28)),2) + POWER((y-(151)),2))) as distance
from table
order by distance desc
fetch first row with ties
Related
There is a tasks table.
id | name | project_id | created | ...
Tasks can be in different projects. I need to return one task from each project with a minimum creation date. Here is my solution
SELECT *
FROM tasks a
JOIN (
SELECT project_id, min(created) as created
FROM tasks
GROUP BY project_id
) b
ON a.project_id=b.project_id AND a.created = b.created;
but if there are points in the project with the same creation dates, then I return two records for one project
To ensure that 1, and only 1, row is returned per project_id a better method is to use row_number() over() where the partition by within the over() clause is similar to what you would have grouped by and the order by controls which row within each partition is given the value of 1. In this case the value of 1 is given to a row with the earliest created date, and further columns can also be referenced as tie-breakers (e.g. using id). Every other row within the partition is given the next integer value so only one row in each partition can be equal to 1. So to limit the final result, use a derived table (subquery) followed by a where clause that restricts the result to the first row per partition i.e. where rn = 1.
SELECT
*
FROM (SELECT *
, row_number() over(partition by project_id order by created, id) as rn
FROM tasks
) AS derived
WHERE rn = 1
nb: to get the most recent row reverse the direction of ordering on the date column
Not only will this technique ensure only 1 row per partition is returned it also requires fewer passes through the data (than your original approach), so it is efficient as well.
tip: if you did want to get more than 1 row per partition returned then use rank() or dense_rank() instead of row_number() - because the ranking functions will recognize rows of equal rank and hence return the same rank value. i.e. more than 1 row could get a rank value of 1
the column code has values that have duplicate on it , i do want to remove the duplicate of that row.
for example i want to remove the duplicates of column code as well the row that has duplicate on it. it doesent matter if the other column has duplicate but i do want to base it on the code column. what sql query can i use.? Thank you
this is the table I am working to.
as you can see there are isdeleted column that has value of 1 on them. I only want the recored with a value of 0 on them
here is a sample record, in here you can see that row 1 has a isdeleted value of 1, which mean that this record is deleted and i only need the row 2 of this code.
You could use the windowing function ROW_NUMBER() to single out the last entry per code like in:
SELECT code, shortdesc, longdesc, isobsolete, effectivefromdate
FROM (
SELECT ROW_NUMBER() OVER(PARTITION BY code ORDER BY effectivefromdate DESC) AS rn, *
FROM CodingSuite_STG
WHERE isobsolete=1 AND isdeleted=0
) AS cs
WHERE rn=1
ORDER BY effectivefromdate
Explanation:
Core of the operation is a "sub-query". That is a "table-like" expression generated by having a SELECT clause surrounded by parentheses and followed by a table name like:
( SELECT * FROM CodingSuite_STG WHERE iobsolete=1 ) AS cs
For the outer SELECT it will appear like a table with the name "cs".
Within this sub-query I placed a special function (a "window function") consisting of two parts:
ROWN_NUMBER() OVER ( PARTITION BY code ORDER BY effectivefromdate DESC) AS rn
The ROW_NUMBER() function returns a sequential number for a certain "window" of records defined by the immediately following OVER ( ... ) clause. The PARTITION BY inside it defines a group division scheme (similar to GROUP BY), so the row numbers start from 1 for each partitioned group. ORDER BY determines the numbering order within each group. So, with entries having the same code value ROW_NUMBER() will supply the number sequence 1, 2, 3... for each record, with 1 being assigned to the record with the highest value of effectivefromdate because of ORDER BY effectivefromdate DESC.
All we need to do in the outer SELECT clause is to pick up those records from the sub-query cs that have an rn-value of 1 and we're done!
I have a table Trial_tb with columns p_id,t_number and rundate.
Sample values:
p_id|t_number|rundate
=====================
111|333 |1/7/2016||
111|333 |1/1/2016||
222|888 |1/8/2016||
222|444 |1/2/2016||
666|888 |1/6/2016||
555|777 |1/5/2016||
pid and tnumber are key columns. I need fetch values such that the result should not have any record in which pid-tnumber combination are duplicated. For example there is duplication for 111|333 and hence not valid. The query should fetch all other than first two records.
I wrote below script but it fetches only the last record. :(
select rundate,p_id,t_number from
(
select rundate,p_id,t_number,
count(p_id) over (partition by p_id) PCnt,
count(t_number) over (partition by t_number) TCnt
from trialtb
)a
where a.PCnt=1 and a.TCnt=1
The having clause is ideal for this job. Having allows you to filter on aggregated records.
-- Finding unique combinations.
SELECT
p_id,
t_number
FROM
trialtb
GROUP BY
p_id,
t_number
HAVING
COUNT(*) = 1
;
This query returns combinations of p_id and t_number that occur only once.
If you want to include rundate you could add MAX(rundate) AS rundate to the select clause. Because you are only looking at unique occurrences the max or min would always be the same.
Do you mean:
select
p_id,t_number
from
trialtb
group by
p_id,t_number
having
count(*) = 1
or do you need the run date too?
select
p_id,t_number,max(rundate)
from
trialtb
group by
p_id,t_number
having
count(*) = 1
Seeing as you are only looking items with one result using max or min should work fine
I have a complex query and which may return more than one record per group. There is a field that has a numeric sequential number. If in a group there is more than one record returned I just want the record with the highest sequential number.
I’ve tried using the SQL MAX function, but if I try to add more than one field it returns all records, instead of the one with the highest sequential field in that group.
I am trying to accomplish this in MS Access.
Edit: 4/5/11
Trying to create a table as an example of what I am trying to do
I have the following table:
tblItemTrans
ItemID(PK)
Eventseq(PK)
ItemTypeID
UserID
Eventseq is a number field that increments for each ItemID. (Don’t ask me why, that’s how the table was created.) Each ItemID can have one or many Evenseq’s. I only need the last record (max(Eventseq)) PER each ItemTypeID.
Hope this helps any.
SELECT A.*
FROM YourTable A
INNER JOIN (SELECT GroupColumn, MAX(SequentialColumn) MaxSeq
FROM YourTable
GROUP BY GroupColumn) B
ON A.GroupColumn = B.GroupColumn AND A.SequentialColumn = B.MaxSeq
If your SequentialNumber is an ID (unique across the table), then you could use
select *
from tbl
where seqnum in (
select max(seqnum) from tbl
group by groupcolumn)
If it is not, an alternative to Lamak's query is the Access domain function DMAX
select *
from tbl
where seqnum = DMAX("seqnum", "tbl", "groupcolumn='" & groupcolumn & "'")
Note: if the groupcolumn is a date, use # instead of single quotes ' in the above, if it is a numeric, remove the single quotes.
How can i get the nth row position from table without using limit ?
I have a table with four fields id,name,country,description. The query is returning by condition country = 'asia'. The total number of records is more than hundred. Now what i need is if i hav a name 'test' in 23rd position in table then how can i get the position 23rd without using limit and auto increment id ( auto id doesn't give the exact position where i am using a condition over my query)
name should not contain the duplicate record.
I just want the position to check through another query (for pagination).
Is there any function available in mysql to achieve this with out using limit?
I have got some idea through this but i cant get my expected mysql result through the answers.
Thanks.
Since SQL does not have concept of implicit "row position", you should define the row order by sorting the rows on a column or an expression.
This assumes your row positions are identified by the field id (i. e. rows with higher id come later).
SELECT (
SELECT COUNT(*)
FROM mytable mi
WHERE country = 'asia'
AND mi.id <= mo.id
)
FROM mytable mo
WHERE country = 'asia'
AND name = 'test'