I'm developing a ASP.NET web application that displays some SSRS reports. My application's database is located in a different server from my report's database, considering that reports consume data from both servers there's a linked server in report database server to application's server.
In one of dataset reports I have a query as bellow:
SELECT T.column1, T1.column2
FROM localTable T
JOIN [linkedServer].[databasename].tablename T1 ON T.id = T1.id
There's only 3 reports, so it was ok to replicate [linkedServer].[databasename] when i changed the application to another environment.
My question is: what's the best way to parameterize [linkedServer].[databasename] in order not to need replace all occurrences every time the server and/or database names change?
next to the query field in the dataset, there is a little fx which allows you to enter an expression for the query.
from your example the query would be
= "SELECT T.column1, T1.column2 FROM localTable T JOIN [" + Parameters!ReportParameter2.Value + "].[databasename].tablename T1 ON T.id = T1.id"
or sth in the like.
in a off topic note i would also recommend to never use the server.database.owner.table syntax, but openquery(server, 'query'). this is for performance reasons, as the server.database.owner.table will copy the whole table over and the openquery retrieves only the result of the query.
Related
I am new to using SQL Server from RStudio. I am connected to SQL Server from RStudio and the server has several different projects listed in the below image. For this work I am using odbc library. I am trying to retrieve the tables of a specific project(Project_3960). I have tried dbListTables(conn,"Project_3960") but this command retrieve the tables from all the projects listed in the below Picture. I just want to retrieve the table which are listed in dbo in Project_3690.
The first picture is from RStudio and the second picture is from SQL Management Studio to show the structure of the folders, in case for executing SQL Query.
Thanks
Click on the arrow to the left of the dbo object under Project_3690, and it should show you the tables you have access to. If it does not, then you have a permissions problem and will need to talk with the DBA. That allows you to see them via the GUI. In fact, if you don't already know the names of the tables you should be accessing (such as to follow my code below), then this is the easiest, as they are already filtering out the system and other tables that obscure what you need.
To see them in R code, then dbListTables(conn) will show you all tables, including the ones in the Connections pane I just described but also a lot of system and otherwise-internal tables that you don't need. On my SQL Server instance, it returns over 600 tables, so ... you may not want to do just that, but you can look for specific tables.
For example, if you know you should have tables Table_A and Table_B, then you could do
alltables <- dbListTables(conn)
grep("table_", alltables, value = TRUE, ignore.case = TRUE)
to see all of the table names with that string in its name.
If you do not see tables that you know you need to access, then it is likely that your connection code did not include the specific database, in which case you need something like:
conn <- dbConnect(odbc(), database="Project_3690", uid="...", pwd="...",
server="...", driver = "...")
(Most fields should already be in your connection code, don't use literal ... for your strings.)
One can use a system table to find the other tables:
DBI::dbGetQuery(conn, "select * from information_schema.tables where table_type = 'BASE TABLE' and table_schema = 'dbo'")
# TABLE_CATALOG TABLE_SCHEMA TABLE_NAME TABLE_TYPE
# 1 Project_3690 dbo Table_A BASE TABLE
# 2 Project_3690 dbo Table_B BASE TABLE
# 3 Project_3690 dbo Table_C BASE TABLE
(Notional output but representative of what it should look like.)
Its not quite direct to retrieve the data from SQL server using RStudio when you have different schemas and all are connected to the server. It is easy to view the connected Databases with schema in SQL Server Management Studio but not in RStudio. The easiest way while using Rodbc is to use dot(.) operator and its easy to retrieve the tables of a specific data base is by using "." with dbGetQuery function. I tried dbGetQuery(conn, "select * from project_3690.dbo.AE_ISD ") and it works perfectly fine.
We have started to use the updated System.Web.Providers provided in the Microsoft.AspNet.Providers.Core package from NuGet. We started to migrate our existing users and found performance slowing and then deadlocks occurring. This was with less than 30,000 users (much less than the 1,000,000+ we need to create). When we were calling the provider, it was from multiple threads on each server and there were multiple servers running this same process. This was to be able to create all the users we required as quickly as possible and to simulate the load we expect to see when it goes live.
The logs SQL Server generated for for a deadlock contained the EF generated sql below:
SELECT
[Limit1].[UserId] AS [UserId]
, [Limit1].[ApplicationId] AS [ApplicationId]
, [Limit1].[UserName] AS [UserName]
, [Limit1].[IsAnonymous] AS [IsAnonymous]
, [Limit1].[LastActivityDate] AS [LastActivityDate]
FROM
(SELECT TOP (1)
[Extent1].[UserId] AS [UserId]
, [Extent1].[ApplicationId] AS [ApplicationId]
, [Extent1].[UserName] AS [UserName]
, [Extent1].[IsAnonymous] AS [IsAnonymous]
, [Extent1].[LastActivityDate] AS [LastActivityDate]
FROM
[dbo].[Users] AS [Extent1]
INNER JOIN [dbo].[Applications] AS [Extent2] ON [Extent1].[ApplicationId] = [Extent2].[ApplicationId]
WHERE
((LOWER([Extent2].[ApplicationName])) = (LOWER(#p__linq__0)))
AND ((LOWER([Extent1].[UserName])) = (LOWER(#p__linq__1)))
) AS [Limit1]
We ran the query manually and the execution plan said that it was performing a table scan even though there was an underlying index. The reason for this is the use of LOWER([Extent1].[UserName]).
We looked at the provider code to see if we were doing something wrong or if there was a way to either intercept or replace the database access code. We didn't see any options to do this but we did find the source of the LOWER issue, .ToLower() is being called on both the column and parameter.
return (from u in ctx.Users
join a in ctx.Applications on u.ApplicationId equals a.ApplicationId into a
where (a.ApplicationName.ToLower() == applicationName.ToLower()) && (u.UserName.ToLower() == userName.ToLower())
select u).FirstOrDefault<User>();
Does anyone know of a way that we change the behaviour of the provider to not use .ToLower() so allowing the index to be used?
You can create an index on lower(username) per Sql Server : Lower function on Indexed Column
ALTER TABLE dbo.users ADD LowerFieldName AS LOWER(username) PERSISTED
CREATE NONCLUSTERED INDEX IX_users_LowerFieldName_ ON dbo.users(LowerFieldName)
I was using the System.Web.Providers.DefaultMembershipProvider membership provider too but found that it was really slow. I changed to the System.Web.Security.SqlMembershipProvider and found it to be much faster (>5 times faster).
This tutorial shows you how to set up the SQL database that you need to use the SqlMembershipProvider http://weblogs.asp.net/sukumarraju/archive/2009/10/02/installing-asp-net-membership-services-database-in-sql-server-expreess.aspx
This database that is auto generated uses stored procedures which may or may not be an issue for your DB guys.
I want to retrieve some data to use it in my grid, but the problem is my database design contains two databases.
So, can I retrieve data from more than database, to use it at one grid ?
I use ASP.Net, C#.Net 4, Microsoft SQL Server 2008 R2
SQL Server knows 4 part object names. The first part is the (linked) server name. The second part is the database name. third and fourth are schema and object name.
Assuming your databases are on the same server you can just write a query like:
SELECT *
FROM Database1.dbo.Table1 t1
JOIN Database2.dbo.Table2 t2
ON t1.column = t2.column;
There are several ways depending on your architecture.
If your databases are deployed in the same machine you can select data from two different databases like this:
SELECT a.userID, b.usersFirstName, b.usersLastName
FROM databaseA.dbo.TableA a
inner join database B.dbo.TableB b ON a.userID=b.userID
Of course you should have permission in both databases.
You can check here for more information: http://forums.asp.net/t/1254974.aspx/1
I've got this query
UPDATE linkeddb...table SET field1 = 'Y' WHERE column1 = '1234'
This takes 23 seconds to select and update one row
But if I use openquery (which I don't want to) then it only takes half a second.
The reason I don't want to use openquery is so I can add parameters to my query securely and be safe from SQL injections.
Does anyone know of any reason for it to be running so slowly?
Here's a thought as an alternative. Create a stored procedure on the remote server to perform the update and then call that procedure from your local instance.
/* On remote server */
create procedure UpdateTable
#field1 char(1),
#column1 varchar(50)
as
update table
set field1 = #field1
where column1 = #column1
go
/* On local server */
exec linkeddb...UpdateTable #field1 = 'Y', #column1 = '1234'
If you're looking for the why, here's a possibility from Linchi Shea's Blog:
To create the best query plans when
you are using a table on a linked
server, the query processor must have
data distribution statistics from the
linked server. Users that have limited
permissions on any columns of the
table might not have sufficient
permissions to obtain all the useful
statistics, and might receive aless
efficient query plan and experience
poor performance. If the linked
serveris an instance of SQL Server, to
obtain all available statistics, the
user must own the table or be a member
of the sysadmin fixed server role, the
db_ownerfixed database role, or the
db_ddladmin fixed database role on the
linkedserver.
(Because of Linchi's post, this clarification has been added to the latest BooksOnline SQL documentation).
In other words, if the linked server is set up with a user that has limited permissions, then SQL can't retrieve accurate statistics for the table and might choose a poor method for executing a query, including retrieving all rows.
Here's a related SO question about linked server query performance. Their conclusion was: use OpenQuery for best performance.
Update: some additional excellent posts about linked server performance from Linchi's blog.
Is column1 primary key? Probably not. Try to select records for update using primary key (where PK_field=xxx), otherwise (sometimes?) all records will be read to find PK for records to update.
Is column1 a varchar field? Is that why are you surrounding the value 1234 with single-quotation marks? Or is that simply a typo in your question?
Without stored procedures, how do you page result sets retrieved from SQL Server in ASP.NET?
You could use LINQ, for instance:
var customerPage = dataContext.Customers.Skip(50).Take(25);
and then display those 25 customers.
See Scott Guthrie's excellent Using LINQ-to-SQL - section 6 - retrieve products with server side paging.
Another option (on SQL Server 2005 and up) is to use ordered CTE's (Common Table Expression) - something like this:
WITH CustomerCTE AS
(
SELECT CustomerID,
ROW_NUMBER() OVER (ORDER BY CustomerID DESC) AS 'RowNum'
FROM Customers
)
SELECT * FROM CustomerCTE
WHERE rownum BETWEEN 150 AND 200
You basically define a CTE over your sort critiera using the ROW_NUMBER function, and then you can pick any number of those at will (here: those between 150 and 200). This is very efficient and very useful server-side paging. Join this CTE with your actual data tables and you can retrieve anything you need!
Marc
PS: okay, so the OP only has SQL Server 2000 at hand, so the CTE won't work :-(
If you cannot update to either SQL Server 2005, or .NET 3.5, I'm afraid your only viable option really is stored procedures. You could do something like this - see this blog post Efficient and DYNAMIC Server-Side paging with SQL Server 2000, or Paging with SQL Server Stored Procedures
The best is to use an ORM which will generate dynamic paging code for you - LINQ To SQL, NHibernate, Entity Framework, SubSonic, etc.
If you have a small result set, you can page on the server using either DataPager, PagedDataSource, or manually using LINQ Skip and Take commands.
(new answer since you're using SQL Server 2000, .NET 2.0, and don't want to use an ORM)
There are two ways to handle paging in SQL Server 2000:
If you have a ID column that's sequential with no holes, you can execute a SQL string that says something like SELECT Name, Title FROM Customers WHERE CustomerID BETWEEN #low and #high - #low and #high being parameters which are calculated based on the page size and page that you're on. More info on that here.
If you don't have a sequential ID, you end up using a minimum ID and ##rowcount to select a range. For instance, SET ##rowcount 20; SELECT Name, Title FROM Customers WHERE CustomerID > #low' - either calculating #low from the page size and page or from the last displayed CustomerID. There's some info on that approach here.
If you have a small dataset, you can page through it in .NET code, but it's less efficient. I'd recommend the PagedDataSource, but if you want to write it yourself you can just read your records from a SqlDataReader into an Array and then use the Array.Range function to page through it.
This is how I handled all of my paging and sorting with AJAX in my ASP.NET 2.0 application.
http://programming.top54u.com/post/AJAX-GridView-Paging-and-Sorting-using-C-sharp-in-ASP-Net.aspx
Well my general approach is usually to create two tables for the results to be paged. The first is an info table that has a search id identity column and has the min and max row numbers. The second table contains the actual results and has an identity column for the row number. I insert into the second table and get the min and max rows and store them in the first table. Then I can page through by selecting just the rows I want. I usually expire the results after 24 hours by using code right before the insert. I usually use a stored procedure to do the inserts for me but you could do it without a stored procedure.
This has the advantage of only performing the more complex sql search once. And the dataset won't change between page displays. It is a snapshot of the data. It also can ease server side sorting. I just have to select those rows in order and reinsert into the second table.