I am trying to use the SKIP(N) function in a linq query. The problem is I need to know the collection size (Count()) inorder to calculate N.
I am having trouble wrapping my head around this query below... How do I get the Collection Size inside the Skip part of the query below ?
var t = from row in db.table where <Clause>
orderby <row> ascending
group row by <row> into A
select A).OrderBy(x => x.Key).Skip(Math.Max(0, <Need to know collection size> - N ).ToDictionary(......
Related
In order to make pagination, I need to order a query list, then take nSize elements skipping nFrom first
I wonder if, from the performance point of view, it's the same ordering by the clause orderby in the query, like this
IList<Product> resul = (
from m in db.Products()
where m.CategoryId==cId
orderby m.Name descending
select m
).Skip(nFrom).Take(nSize).ToList();
or ordering the results, like this
IList<Product> resul = (
from m in db.Products()
where m.CategoryId==cId
select m
).OrderByDescending(m=>m.Name).Skip(nFrom).Take(nSize).ToList();
I guess LINQ makes the same in both cases, but I need make sure in order to use the second option so I can parameterize the order field.
I need to update a column in one table with the results from a select sub-query (and they should ultimately be different). But When I do this, I get the 'ORA-01427: single row sub-query returns more than one row query' error.
Can you please take a look and see what it is that I am overlooking? (I could just be overlooking something simple for all I know)
UPDATE AIRMODEL_NETWORK_SUMMARY ans
SET ANS.NBR_RETURNS = (
SELECT SUM(RQ.RETURN_QTY)
FROM RETURN_QTY RQ JOIN AIRMODEL_NETWORK_SUMMARY ANS ON RQ.LOC_ID = ANS.LOC_ID
WHERE RQ.FSCL_YR_NUM = ans.FSCL_YR_NUM
AND RQ.FSCL_WK_IN_YR_NUM =
ans.FSCL_WK_IN_YR_NUM
GROUP BY ANS.LOC_ID,
ans.FSCL_WK_IN_YR_NUM,
ANS.FSCL_YR_NUM
);
I think that your inner query is not well correlated to the table that you're trying to update. Please look here Oracle SQL: Update a table with data from another table. You should add some kind of a where condition that ties the rows you're trying to update with the values calculated by the inner statement.
My question involves MVC + Linq query. I will try to make it simple without going into the details of the Model, View, etc.. Say I have 2 tables T1 & T2. T1 holds restaurants details & T2 holds restaurants image paths. T2 rows contain restaurantID. Now if T2 has more than one rows of image paths for a Restaurant and I only need the first image path from T2 in the linq query how would I form such query? I tried to simplify the question as in fact I have 6 table joins related to the Restaurants in the query. I formed a view model which only contains the fields I want to display. I am trying to populate the view model in the controller & the query is in the controller obviously.
When I join T2 to the query, I get all the Restaurants details together with the images. But the view repeats the same Restaurant as many times as the number of table rows in T2 which is not what I want. This is the problem from the way I set the query. The query uses joins. I only need the first row from T2 while I get all from the Restaurant details. I failed to find an example for such requirement on the web so far. Your directions will be much appreciated.
Serhat Albayoglu
On your join you can use an into and then in the select you can select the FirstOrDefault
var query = from t in context.T1
join t2 in context.T2 on t.Id equals t2.RestaurantID into tgroup
select
{
t2.FirstOrDefault().path
};
The issue I face that I need after selecting multiple rows,to loop over each row and fetch those who have some related information to the first row.
Example:
select NAME,ENGLISH_GRADE,FRANCE_GRAE
from (some complex query that have order by and returns 100 rows) WHOLE_ROWS
where
//Here I need to loop over WHOLE_ROWS and make something like that:
//if(currentRow.ENGLISH_GRADE==WHOLE_ROWS(0).ENGLISH_GRADE)
//fetch this row
Basically, you need to join your query to itself. You can do with with a subquery factoring clause:
WITH complex_query AS
( ... complex query here ... )
SELECT
FROM complex_query cq1
WHERE cq1.english_grade = ( SELECT english_grade FROM cq1
WHERE rownum = 1 )
Here is a SQL Fiddle. You could also do this with analytics, but those seem to me more difficult to understand.
I'm having a small issue with sorting the data returned from a query, with the aim of getting the oldest updated value in dataset so that I can update only that record. Here's what I'm doing:
WHERE ROWNUM = 1 AND TABLE1.ID != V_IGNOREID
AND TABLE1.LASTREADTIME = (SELECT MIN(TABLE1.LASTREADTIME) FROM TABLE1)
ORDER BY TABLE1.LASTREADTIME DESC;
It makes no difference as to whether the ORDER BY statement is included or not. If I only use the ROWNUM and equality checks, I get data, but it alternates between only two rows, which is why I'm trying to use the LASTREADTIME data (so that I can modify more than these two rows). Anybody have any thoughts on this, or any suggestions as to how I can use the MIN function effectively?
Cheers
select * from (
-- your original select without rownum and with order by
)
WHERE ROWNUM = 1
EDIT some explanation
I think the order by clause is applied on the resultset after the where clause. So if the rownum = 1 is in the same select statement with the order by, then it will be applied first and the order by will order only 1 row, which will be the first row of the unordered resultset.