I have to write two LINQ query,which one returns the TOP 6 rows and the another which return data excluding the TOP 6 rows:
TOP 6:
from m in MyTable
take 6
select m.Foo
I need help how to figure out the second query.
Try MyTable.Skip(6). I don't think there is a way to do this in the query syntax. Read more about Take and Skip here and here.
Use Except (according to your C# like syntax):
var fullList = from m in MyTable select m.Foo;
var top6 = from m in MyTable take 6 select m.Foo;
var top6except = fullList.Except(top6);
This exclude the TOP 6 rows retrieved and not generally the top 6 rows. Use Skip method to achieve the generic "select starting from 7th row"
To take all but the first 6 rows, use Skip():
var allButFirst6 = (from m in MyTable
select m.Foo).Skip(6);
Please note that some LINQ providers require the list to be ordered in order to use Skip and Take. If this is the case, then use OrderBy to order the list before using Skip or Take.
Related
I have two tables, one called STUDENTS and the other CLASSES. I have to select all the students that are from the same class of one student, and this student has his own number id, and through this number id that I have to select everything.
TABLE STUDENTS
nr_rgm
nm_name
nm_father
nm_mother
dt_birth
id_sex
TABLE CLASSES
cd_class
nr_schoolyear
cd_school
cd_degree
nr_series
cd_class
cd_period
So I tried something like that :
SELECT count(*) FROM students, classes WHERE id_sex = 'M' AND
cd_class = (SELECT cd_class FROM classes WHERE nr_rgm = '12150');
But then it points an error, and the error is the follow :
single-row subquery returns more than one row
So, how can I make this work ?
you should use "in" and not "=" when applying subselects.
I think what you really would want to do is to simply join the two tables together rather than issuing a sub select:
SELECT count(*)
FROM students s, classes c
WHERE s.id_sex = 'M' AND c.nr_rgm = '12150' AND s.cd_class = c.cd_class;
This way you just tell the database: Please count all the occurrences where my students.id_sex = 'M' and my classes.nr_rgm = '12150' AND all found studends.cd_class match those of my classes.cd_class.
The reason why your statement above fails is because the ordinary = operation, when not used in a join, will only expect one single value, like you do with s.id_sex='M' while your statement returns multiple values. To cope with that you have to use the IN operator which operates on lists.
However, you can and will achieve the very same with just joining the two tables together, and it will be much more efficient on bigger data sets.
One more note to the example above. If classes.nr_rgm is a field of data type NUMBER, don't use the ' around the value 12150 as it will lead to implicit type conversion. With other words, '12150' is a string and will have to be converted to NUMBER first before doing a comparison.
The issue with the image above is that
I want to apply a bonus share to the shareholders based on the TransLog_Date
Because the shareholder in row 1 has already transferred a portion of his shares to the holder in row 3, his new share value is what shows in row 2 column 5 as 100000
I want the bonus share to be calculated based on the value in row 2, column 5 but not on row 1, column 5.
I have tried several codes in LINQ but getting it wrong as the value is multiplied on all the 3 records which is totally wrong.
var transQuery = (from tq in db.TransactionsLogDbSet
where (tq.TransactionType == TransactionType.PurchaseOfShares)
|| (tq.TransactionType == TransactionType.TransferOfShares)
|| (tq.TransactionType == TransactionType.BonusSharesDeclared)
select tq);
var query = from row in db.TransactionsLogDbSet
group row by row.Transholder_ID into g
select new { Count = g.Count() };
OK, i think I finally got what you want.
Is that right?: Group all rows of some TransactionTypes by the Transholder_ID, then from each group select the row with the maximum Translog_Date, giving you the most recent row per Transholder_ID. Once you have the result of that, you can iterate over it to calculate whatever you need.
from t in db.TransactionLogDbSet
where where tq.TransactionType == TransactionType.PurchaseOfShares || tq.TransactionType == TransactionType.TransferOfShares || tq.TransactionType == TransactionType.BonusSharesDeclared
group t by t.Transholder_ID into g
select (from t1 in g orderby t1.Translog_Date descending select t1).First();
EDIT: I'll continue to edit the following part of my answer as long as we finally arrive at the correct query.
From you last comment so far it follows that you just want to select all rows with a TransLog_Date <= a given DateTime qualifiedDate.
from t in db.TransactionLogDbSet
where t.TransactionLog_Date <= qualifiedDate
select t
Is that it?
I am working in C#.Net and Oracle. i am passing a string to a query. i had used this code for concating all the item id's
List<string> listRetID = new List<string>();
foreach (DataRow row in dtNew.Rows)
{
listRetID.Add(row[3].ToString());
}
This concatination goes above 10,000. so i am getting the error message like this..
ORA-01795: maximum number of expressions in a list is 1000
How to fix this..
The documentation states:
A comma-delimited list of expressions can contain no more than 1000
expressions. A comma-delimited list of sets of expressions can contain
any number of sets, but each set can contain no more than 1000
expressions.
Presumably you're using this string as the contents of in IN (...) restriction, in which case there isn't really anything you can do - this just won't work. A common way to work around this is to generate a dummy table as a subquery or common table expression (CTE) and joining to that, but I'm not sure how you'd translate your List - possibly similar to whatever you're doing with your IN clause. You'd want to end up with your query looking something like:
with tmp_tab as (
select <val1 from list> as val from dual
union all select <val2 from list from dual
union all select <val3 from list from dual
...
)
select <something>
from <your table> yt
join tmp_tab tt on yt.<field> = tt.val
But that requires generating the entire (huge) query including the CTE each time you run it, and there's no opportunity to use bind variables.
You might find something like this approach more palatable.
You can have 10 lists of 1000 items instead of 1 list of 10000 items.
WHERE some_column IN (1,2,...,1000)
OR some_column IN (1001,1002,...2000) -- etc.
Not a C# guy but I would just split the list listRetID in multiple lists or create a list of lists
Then loop through that list of lists and perform the query on each element of the list.
What is the intent of your query?
It looks like you are selecting rows that have some column equal to the 3rd column of one of the records of some query.
The correct way of doing this is either an SQL join or a subquery. There is absolutely no need to bring this into C# code. For example, using a subquery you can write something like this:
SELECT *
FROM atable
WHERE afield IN (
SELECT field3
FROM someothertable)
I have many tables.But there are Two columns common in each table.
They are RegNo and Total.Now i want the values of all the total column for a particular RegNo.
I can get that in different queries like this.
query=from k in db.MyTable1 where K.regNo=1 select k.Total
query2=from k in db.MyTable2 where K.regNo=1 select k.Total
This way but i want to do this and get the Summation of all Total's Column using one single Query
Please guide.
You can do it this way.
var itemCounts = (from k in db.MyTable1 where k.RegNO==1 select k.Total)
.Union(from k in db.MyTable2 where k.RegNO==1 select k.Total);
TotalOfAll=itemCounts.Sum();
and using the sum method you can get the summation of all the Values in the query.
I need to get the result of concatenating 2 similar querys' resulsets. For some reason had to split the original query in 2, both with their corresponding order by clause. Should be something like (this is an oversimplification of the original queries)
Query1: Select name, age from person where age=10
Resultset1:
Person1, 10
Person3, 10
Query2: Select name, age from person where age=20
Resultset1:
Person2, 20
Person6, 20
The expected result:
Person1, 10
Person3, 10
Person2, 20
Person6, 20
I can not simply use Query1 UNION Query2.
Below the 2 original querys:
(#1)
select cp.CP_ID, cpi.CI_DESCRIPCION, cp.CP_CODIGOJERARQUIZADO, cp.CP_ESGASTO as gasto, cp.CP_CONCEPTOPADRE, LEVEL
from TGCCP_ConceptoPagoIng cp
left join tgcci_ConceptoPagoIngIdioma cpi on cpi.CI_IDCONCEPTOPAGOING = cp.CP_ID and cpi.CI_IDIDIOMA = 1
start with ((CP_CONCEPTOPADRE is null) and (**cp.CP_ESGASTO = 1**))
connect by prior cp.CP_ID = cp.CP_CONCEPTOPADRE
order siblings by CP_CODIGOJERARQUIZADO
(#2)
select cp.CP_ID, cpi.CI_DESCRIPCION, cp.CP_CODIGOJERARQUIZADO, cp.CP_ESGASTO as gasto, cp.CP_CONCEPTOPADRE, LEVEL
from TGCCP_ConceptoPagoIng cp
left join tgcci_ConceptoPagoIngIdioma cpi on cpi.CI_IDCONCEPTOPAGOING = cp.CP_ID and cpi.CI_IDIDIOMA = 1
start with ((CP_CONCEPTOPADRE is null) and (**cp.CP_ESGASTO = 2**))
connect by prior cp.CP_ID = cp.CP_CONCEPTOPADRE
order siblings by CP_CODIGOJERARQUIZADO
I think you want a
select * from ( first query )
UNION ALL
select * from ( second query )
Where first query and second query are the queries from above, so you are turning them into subqueries, thus preserving the order by clauses.
OK, well, I'm not fully certain why you need it this way, but if Oracle won't allow you to do a UNION, or it screws up the ordering when you do, I would try creating a pipelined table function.
An example here
Basically, you'd create a procedure that ran both queries, first one, then the other, putting the results of each into the returned dataset.
It looks like you are looking for a MULTISET UNION. Which can only be used from version 10 upwards.
Regards,
Rob.
You could combine your queries as subqueries and do a single order by on the outer query:
select * from (
<query 1 with its order by>
UNION ALL
<query 2 with its order by>
)
order by column1, column2;
Alternatively, you can implement in PL/SQL the equivalent of a sort merge join with two cursors, but that's unnecessarily complicated.
this solution works perfectly:
select * from ( first query )
UNION ALL
select * from ( second query )
I appreciate everyone that have taken the time to answer.
regards.
For your example:
Select name, age from person where age in (10,20)
or
Select name, age from person where age = 10 or age = 20
However I'm guessing this is not what you need :)