I have modified the nerd dinner example to find locations in the vicinity of specified position. When selecting from a flat table performance is good, but I wanted to split up the tables so I have a generic coordinates table (SDB_Geography) and also join in a table with specific data for what i call the entity type (HB_Entity).
I have made a new model called HbEntityModel which stores entity, hb and geography "sub models". Now the problem is that this query takes around 5 seconds to execute. I figured I would get a slight performance decrease by doing this but 5 seconds is just ridiculous. Any ideas on how to improve the performance with currrent table setup or do i have to go back to a monstrous flat table?
public IEnumerable<HbEntityModel> FindByLocation(float latitude, float longitude)
{
return (from entity in db.SDB_Entity.AsEnumerable()
join nearest in NearestEntities(latitude, longitude, 2)
on entity.EntityId equals nearest.EntityId
join hb in db.HB_Entity
on entity.EntityId equals hb.EntityId
join geo in db.SDB_Geography
on entity.GeographyId equals geo.GeographyId
select new HbEntityModel(entity, hb, geo)).AsEnumerable();
}
UPDATE
All tables contains around 14000 records.
SDB_Entity 1:0/1 SDB_Geography
SDB_Entity 1:0/1 HB_Entity
The search yields around 70 HbEntityModels.
If selecting from single table the same query takes 0.3s, using IQueryable instead of IEnumerable.
I found out how to do it with some help from Robban". See this post.
I rewrote the function to use a parameterless constructor and could then use IQueryable.
public IQueryable<HbEntityModel> FindByLocation(float latitude, float longitude)
{
return (from entity in db.SDB_Entity
join nearest in NearestEntities(latitude, longitude, 2)
on entity.EntityId equals nearest.EntityId
join hb in db.HB_Entity
on entity.EntityId equals hb.EntityId
join geo in db.SDB_Geography
on entity.GeographyId equals geo.GeographyId
select new HbEntityModel() { Shared=entity, Specific=hb, Geography=geo }).AsQueryable();
}
The query now takes around 0.4 seconds to execute which is somewhat acceptable. Hopefully things will be faster when my mean machine arrives. If someone could give me hints on how to improve the query, use a stored procedure or setup some index, i would be more than grateful.
Related
I am trying to get a list from the database containing two or more lists inside that list.(using .net core, entity framework).Assume I have two table call header and details table.
Header Table
Detail Table
And I want the result like this:
{
"data":[
{
"Country":"Singapore",
"Hospital_List":[
{
"Hospital_Name":"SG Host A"
},
{
"Hospital_Name":"SG Host A"
}
]
},
{
}
]
}
I only know two ways to get the result like this,First Way, select Country list data with blank Hospital list as List,then for loop that list to select related Hospital list from db again.
And Second Way,select Country list data with blank Hospital list as IQueryable List,and then select related Hospital list via jointing with Hospital Table.So my question is
Which way should i used to get higher performance? And Is any other way?
Please remember there has a lot of field and data in my real table.
For loop give give you the lowest perfomance, because you will create SQL query for each iteration. Instead of this, try following solution:
from hospital in hospitals
group hospital by hospital.CID into gh
join country in countries
on gh.FirstOrDefault().CID equals country.CID
select new
{
Country = country.Country,
Hospital_List = from h in gh select h
}
EDITED:
And if your model created right you can use this code:
from hospital in hospitals
join country in countries
on hospital.Country equals country
group hospital by hospital.CID into gh
select new
{
Country = from h in gh select h.Country.Country,
Hospital_List = from h in gh select h
}
The AdventureWorksDW has the construct of the Financial Reporting Fact table. I have a similar fact table where the fact contains only the FK to the dimension tables and a value. The measure gets it's context from an DimAccount dimension. Are there any code samples that show how to do a simple ratio in a calculated member between two measures of the AdventureWorks Financial Reporting sample?
So basically I would like to see say Total Long term Debt / Total Assets from AdventureWorksDW? What I need is the expression or MDX.
Thanks in advance.
Use a query like this:
with member [Account].[Accounts].[Balance Sheet].[Dept by Assets] as
IIf([Account].[Accounts].[Assets] <> 0,
[Account].[Accounts].[Long Term Liabilities] / [Account].[Accounts].[Assets],
null
)
,format_string = "0.00%"
select {
[Account].[Accounts].[Assets],
[Account].[Accounts].[Long Term Liabilities],
[Account].[Accounts].[Dept by Assets]
}
on columns,
{ [Measures].[Amount] }
on rows
from [Adventure Works]
You can define members in any hierarchy, not only in the measures. In the definition, you should use the parent member before the name of the new member, to tell AS the position in the hierarchy. This is more important for CREATE MEMBER in the cube calculation script than for WITH MEMBER, as it influences the position where the client tool will display it.
Hi Can any one help me out of this query forming logic
SELECT C.CPPID, c.CPP_AMT_MANUAL
FROM CPP_PRCNT CC,CPP_VIEW c
WHERE
CC.CPPYR IN (
SELECT C.YEAR FROM CPP_VIEW_VIEW C WHERE UPPER(C.CPPNO) = UPPER('123')
AND C.CPP_CODE ='CPP000000000053'
and TO_CHAR(c.CPP_DATE,'YYYY/Mon')='2012/Nov'
)
AND UPPER(C.CPPNO) = UPPER('123')
AND C.CPP_CODE ='CPP000000000053'
and TO_CHAR(c.CPP_DATE,'YYYY/Mon') = '2012/Nov';
Please Correct me if i formed wrong query structure, in terms of query Performance and Standards. Thanks in Advance
If you have some indexes or partitioned tables I would not use functions on columns but on variables, to be able to use indexes/select partitions.
Also I use ANSI 92 SQL syntax. You don't specify(or not directly) a join contition between cpp_prcnt and cpp_view so it is actually a cartesian product(cross join)
SELECT C.CPPID, c.CPP_AMT_MANUAL
FROM CPP_PRCNT CC
CROSS JOIN CPP_VIEW c
WHERE
CC.CPPYR IN (
SELECT C.YEAR
FROM CPP_VIEW_VIEW C
WHERE C.CPPNO = '123'
AND C.CPP_CODE ='CPP000000000053'
AND trunc(c.CPP_DATE,'MM')=to_date('2012/Nov','YYYY/Mon')
)
AND C.CPPNO = '123'
AND C.CPP_CODE ='CPP000000000053'
AND trunc(c.CPP_DATE,'MM')=to_date('2012/Nov','YYYY/Mon')
If you show us the definition of cpp_view_view(seems to be a view over cpp_view), the definition(if simple) of CPP_VIEW and what you're trying to achieve, I bet there are more things to be improved/fixed.
There are a couple of things you could improve:
if possible, get rid of the UPPER() in the comparison - this will render any indices useless. If that's not possible, consider a function-based index on UPPER(CPPNO)
do not convert your DATE column to a string to compare it with a string - do it the other way round (i.e. convert your string to a date => only one conversion needed instead of one per table row, use of indices possible)
play around with EXISTS instead of IN, as suggested by Dileep - might be faster
I have a database with customers orders.
I want to use Linq (to EF) to query the db to bring back the last(most recent) 3,4...n orders for every customer.
Note:
Customer 1 may have just made 12 orders in the last hr; but customer 2 may not have made any since last week.
I cant for the life of me work out how to write query in linq (lambda expressions) to get the data set back.
Any good ideas?
Edit:
Customers and orders is a simplification. The table I am querying is actually a record of outbound messages to various web services. It just seemed easer to describe as customers and orders. The relationship is the same.
I am building a task that checks the last n messages for each web service to see if there were any failures. We are wanting a semi real time Health status of the webservices.
#CoreySunwold
My table Looks a bit like this:
MessageID, WebserviceID, SentTime, Status, Message, Error,
Or from a customer/order context if it makes it easer:
OrderID, CustomerID, StatusChangedDate, Status, WidgetName, Comments
Edit 2:
I eventually worked out something
(Hat tip to #StephenChung who basically came up with the exact same, but in classic linq)
var q = myTable.Where(d => d.EndTime > DateTime.Now.AddDays(-1))
.GroupBy(g => g.ConfigID)
.Select(g =>new
{
ConfigID = g.Key,
Data = g.OrderByDescending(d => d.EndTime)
.Take(3).Select(s => new
{
s.Status,
s.SentTime
})
}).ToList();
It does take a while to execute. So I am not sure if this is the most efficient expression.
This should give the last 3 orders of each customer (if having orders at all):
from o in db.Orders
group o by o.CustomerID into g
select new {
CustomerID=g.Key,
LastOrders=g.OrderByDescending(o => o.TimeEntered).Take(3).ToList()
}
However, I suspect this will force the database to return the entire Orders table before picking out the last 3 for each customer. Check the SQL generated.
If you need to optimize, you'll have to manually construct a SQL to only return up to the last 3, then make it into a view.
You can use SelectMany for this purpose:
customers.SelectMany(x=>x.orders.OrderByDescending(y=>y.Date).Take(n)).ToList();
How about this? I know it'll work with regular collections but don't know about EF.
yourCollection.OrderByDescending(item=>item.Date).Take(n);
var ordersByCustomer =
db.Customers.Select(c=>c.Orders.OrderByDescending(o=>o.OrderID).Take(n));
This will return the orders grouped by customer.
var orders = orders.Where(x => x.CustomerID == 1).OrderByDescending(x=>x.Date).Take(4);
This will take last 4 orders. Specific query depends on your table / entity structure.
Btw: You can take x as a order. So you can read it like: Get orders where order.CustomerID is equal to 1, OrderThem by order.Date and take first 4 'rows'.
Somebody might correct me here, but i think doing this is linq with a single query is probably very difficult if not impossible. I would use a store procedure and something like this
select
*
,RANK() OVER (PARTITION BY c.id ORDER BY o.order_time DESC) AS 'RANK'
from
customers c
inner join
order o
on
o.cust_id = c.id
where
RANK < 10 -- this is "n"
I've not used this syntax for a while so it might not be quite right, but if i understand the question then i think this is the best approach.
How do I go about writing the relational algebra for this SQL query?
Select patient.name,
patient.ward,
medicine.name,
prescription.quantity,
prescription.frequency
From patient, medicine, prescription
Where prescription.frequency = "3perday"
AND prescription.end-date="08-06-2010"
AND canceled = "Y"
Relations...
prescription
prescription-ref
patient-ref
medicine-ref
quantity
frequency
end-date
cancelled (Y/N))
medicine
medicine-ref
name
patient
Patient-ref
name
ward
I will just point you out the operators you should use
Projection (π)
π(a1,...,an): The result is defined as the set that is obtained when all tuples in R are restricted to the set {a1,...,an}.
For example π(name) on your patient table would be the same as SELECT name FROM patient
Selection (σ)
σ(condition): Selects all those tuples in R for which condition holds.
For example σ(frequency = "1perweek") on your prescription table would be the same as SELECT * FROM prescription WHERE frequency = "1perweek"
Cross product(X)
R X S: The result is the cross product between R and S.
For example patient X prescription would be SELECT * FROM patient,prescription
You can combine these operands to solve your exercise. Try posting your attempt if you have any issues.
Note: I did not include the natural join as there are no joins. The cross product should be enough for this exercise.
An example would be something like the following. This is only if you accidentally left out the joins between patient, medicine, and prescription. If not, you will be looking for cross product (which seems like a bad idea in this case...) as mentioned by Lombo. I gave example joins that may fit your tables marked as "???". If you could include the layout of your tables that would be helpful.
I also assume that canceled comes from prescription since it is not prefixed.
Edit: If you need it in standard RA form, it's pretty easy to get from a diagram.
alt text http://img532.imageshack.us/img532/8589/diagram1b.jpg