Comments on: Querying With NHibernate http://davybrion.com/blog/2008/10/querying-with-nhibernate/ Trying to walk that thin line between intelligence and ignorance Tue, 16 Mar 2010 21:33:15 +0100 http://wordpress.org/?v=2.9.2 hourly 1 By: Davy Brion http://davybrion.com/blog/2008/10/querying-with-nhibernate/comment-page-1/#comment-3234 Davy Brion Mon, 06 Oct 2008 07:08:50 +0000 http://davybrion.com/blog/?p=480#comment-3234 heh, now this is interesting... one of our database specialists at work told me that subqueries were indeed not the best way to fetch the data so we compared the performance of the query with the subqueries, compared to one that uses only joins (and some variations on that) in each case, the one with subqueries performed better :) i think it's because the resultset of the subqueries is in this case the same for each row in the main query. if the subqueries where using values of the rows in the main query, the join approach would probably be a lot faster i think heh, now this is interesting… one of our database specialists at work told me that subqueries were indeed not the best way to fetch the data

so we compared the performance of the query with the subqueries, compared to one that uses only joins (and some variations on that)

in each case, the one with subqueries performed better :)

i think it’s because the resultset of the subqueries is in this case the same for each row in the main query. if the subqueries where using values of the rows in the main query, the join approach would probably be a lot faster i think

]]> By: Reflective Perspective - Chris Alcock » The Morning Brew #194 http://davybrion.com/blog/2008/10/querying-with-nhibernate/comment-page-1/#comment-3233 Reflective Perspective - Chris Alcock » The Morning Brew #194 Mon, 06 Oct 2008 07:05:46 +0000 http://davybrion.com/blog/?p=480#comment-3233 [...] Querying With NHibernate - Davy Brion explores the construction of complex queries in NHibernate using the criteria API, including looking at creating sub queries, and compares the underlying SQL to a hand crafted original. [...] [...] Querying With NHibernate – Davy Brion explores the construction of complex queries in NHibernate using the criteria API, including looking at creating sub queries, and compares the underlying SQL to a hand crafted original. [...]

]]> By: Davy Brion http://davybrion.com/blog/2008/10/querying-with-nhibernate/comment-page-1/#comment-3195 Davy Brion Sun, 05 Oct 2008 11:37:08 +0000 http://davybrion.com/blog/?p=480#comment-3195 yeah, i'd usually try to do it with joins instead of any subqueries as well. But as far as i know (and if someone can correct this, please do so) you can only join on associations that have been mapped with NHibernate. So joining on 'dynamically' composed resultsets is something that is not possible, unless i'm mistaken. Maybe someone else can shed more light on this :) Having said that, i'd like to know which aproach is better: the joins or the subqueries. Theoritically speaking, i'd think the join approach is better. But these days, you're never really sure how the DB is going to optimize the query when it's actually being executed so i wouldn't be surprised if the subquery approach turns out to be just as fast as the joined approach. yeah, i’d usually try to do it with joins instead of any subqueries as well. But as far as i know (and if someone can correct this, please do so) you can only join on associations that have been mapped with NHibernate. So joining on ‘dynamically’ composed resultsets is something that is not possible, unless i’m mistaken. Maybe someone else can shed more light on this :)

Having said that, i’d like to know which aproach is better: the joins or the subqueries. Theoritically speaking, i’d think the join approach is better. But these days, you’re never really sure how the DB is going to optimize the query when it’s actually being executed so i wouldn’t be surprised if the subquery approach turns out to be just as fast as the joined approach.

]]> By: disco stu http://davybrion.com/blog/2008/10/querying-with-nhibernate/comment-page-1/#comment-3194 disco stu Sun, 05 Oct 2008 11:27:11 +0000 http://davybrion.com/blog/?p=480#comment-3194 scratch that! => like this <code>select customer.CustomerId, customer.CompanyName, customer.ContactName, customer.ContactTitle, customer.Address, customer.City, customer.Region, customer.PostalCode, customer.Country, customer.Phone, customer.Fax from Customers Customer join ( select distinct Orders.CustomerID from Orders join [Order Details] on [Order Details].OrderID = Orders.OrderID where [Order Details].ProductID = 24) ProductCustomer on ProductCustomer.CustomerID = Customer.ID</code> scratch that! => like this

select
customer.CustomerId,
customer.CompanyName,
customer.ContactName,
customer.ContactTitle,
customer.Address,
customer.City,
customer.Region,
customer.PostalCode,
customer.Country,
customer.Phone,
customer.Fax
from
Customers Customer
join (
select distinct
Orders.CustomerID
from
Orders
join [Order Details] on [Order Details].OrderID = Orders.OrderID
where
[Order Details].ProductID = 24) ProductCustomer on ProductCustomer.CustomerID = Customer.ID

]]> By: disco stu http://davybrion.com/blog/2008/10/querying-with-nhibernate/comment-page-1/#comment-3193 disco stu Sun, 05 Oct 2008 11:25:47 +0000 http://davybrion.com/blog/?p=480#comment-3193 Disco Stu would do it like this: <code>select customer.CustomerId, customer.CompanyName, customer.ContactName, customer.ContactTitle, customer.Address, customer.City, customer.Region, customer.PostalCode, customer.Country, customer.Phone, customer.Fax from Customers Customer join ( select Orders.CustomerID from Orders join [Order Details] on [Order Details].OrderID = Orders.OrderID where [Order Details].ProductID = 24 group by Orders.CustomerID) ProductCustomer on ProductCustomer.CustomerID = Customer.ID</code> Disco Stu would do it like this:
select
customer.CustomerId,
customer.CompanyName,
customer.ContactName,
customer.ContactTitle,
customer.Address,
customer.City,
customer.Region,
customer.PostalCode,
customer.Country,
customer.Phone,
customer.Fax
from
Customers Customer
join (
select
Orders.CustomerID
from
Orders
join [Order Details] on [Order Details].OrderID = Orders.OrderID
where
[Order Details].ProductID = 24
group by
Orders.CustomerID) ProductCustomer on ProductCustomer.CustomerID = Customer.ID

]]> By: Querying With NHibernate - NHibernate blog - NHibernate Forge http://davybrion.com/blog/2008/10/querying-with-nhibernate/comment-page-1/#comment-3191 Querying With NHibernate - NHibernate blog - NHibernate Forge Sun, 05 Oct 2008 11:06:09 +0000 http://davybrion.com/blog/?p=480#comment-3191 [...] NOTE: this was originally posted on my own blog [...] [...] NOTE: this was originally posted on my own blog [...]

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