SQL proxy/alias for SQL Server Express - sql-server

I can't find what I need or I don't know what to search.Because we are a large team with different setup in our locals, if is possible somehow to enforce connection strings to be persistent across our locals.
Example: In config files
<connectionStrings>
<add name="SomeEntities"
connectionString="data source=.\SQLEXPRESS;initial catalog=tests;...rest of it..."/>
</connectionStrings>
As in my case, because I installed SQL DEVELOPER (version is irrelevant) my local connection will be "data source=.\;initial catalog=tests;...rest of it..."
Is it possible to set a proxy in SQL Server Configuration Manager for
<SQLSERVERNAME>\SQLEXPRESS to point on my local <SQLSERVERNAME>\
I'm not looking to install SQL Server Express, I want to setup a PROXY that
will help the team to use SQLEXPRESS connection string to work on any
installed SQL Server versions.
UPDATE:
Based on comments and responses, it's possible.
Prerequisites:
TCP/IP protocol must be enable for the instance (in my case port 1433)
To check go in CMD => netstat -an |find "1433"
Setup in SQL SERVER Configuration Manger:
Thank you for the help!

I am not sure if it is the same case that experimented, but in the past, we had a scenario where every developer was using their own name of MS SQL Server instance, we decided to set a standard name in the connectionstring and everyone has configured an alias inside SQL Server Configuration Manager, the steps are:
Enter MS SQL Server Configuration Manager.
Go to SQL Native Client XX Configuration and click in Aliases
Create a new Alias, here you should name it with the standard name that you have registered inside your connection string, inside the Protocol set TCP/IP and later in Server section, you should set up the current name of your local instance.
After that, you have completed the previous step you should be able to connect your local instance through the name that you have defined in the alias.

What are you talking about is called alias:
Create or Delete a Server Alias for Use by a Client
You can create an alias with name SQLSERVERNAME\SQLEXPRESS which will point to localhost and vice versa. Alias should be created on client machine.

Related

SQL Server connection string windows 7 and windows 10 - Named Pipes Provider, error 40 [duplicate]

I can't seem to connect to my database from a site. I get this error:
Named Pipes Provider, error: 40 - Could not open a connection to SQL Server
I tried using the local IP address to connect as well as a public one. I've tried:
Yes, the site can communicate with the server
Named pipes/TCP is enabled.
Remote connections are allowed.
Windows Firewall is off
Created an exception for port 1433 in Windows Firewall.
Enabled everything in SQL Server Configuration Manager.
What else can I do here?
Solving this problem is very easy:
Go to control panel.
search for services.
Open Local services window from your search results
Restart your MSSQLSERVER service.
Screenshot of the steps:
And the simplest solution - check if your slash is back...
I spent about an hour trying to figure out what's wrong with SERVER/INSTANCENAME when everything is configured correctly, named pipes, user access rights... and suddenly it struck me, it's not a slash, it's a backslash (\).
The horror, the shame...
It's a three step process really after installing SQL Server:
Enable Named Pipes
SQL Config Manager --> SQL Server Network Consif --> Protocols --> Named Pipes --> Right-click --> Restart
Restart the server
SQL Config Manager --> SQL Server Services --> SQL Server (SQLEXPRESS) --> Right-click --> Restart
Use proper server and instance names (both are needed!)
Typically this would be .\SQLEXPRESS, for example see the screenshot from QueryExpress connection dialog.
There you have it.
I had just installed SQL SERVER 2012 developer. When I was creating my first SSIS package, I received this pipes error when I was trying to create a data connection task in SQL Server 2012 Data Tools in the Connection Manager box. I resolved with the help of the post above.
If choose a named instance and you call your named instance SSQDatabase1 and your pc's name is PCX1. You must enter PCX1\SSQDatabase1 not just SSQDatabase1
or you will receive the named pipes error.
A thread on MSDN Social, Re: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server, has a pretty decent list of possible issues that are related to your error. You may want to see if any of them could be what you're experiencing.
Incorrect connection string, such as using SqlExpress
Named Pipes(NP) was not enabled on the SQL instance
Remote connection was not enabled
Server not started, or point to not a real server in your connection string
Other reasons such as incorrect security context
try basic connectivity tests between the two machines you are working on
i Just enabled TCP/IP,VIA,Named Pipes in Sql Server Configuration manager , My problem got solved refer this for more info Resolving Named Pipes Error 40
Use SERVER\\ INSTANCE NAME .Using double backslash in my project solved my problem.
Thanks to Damian...
TCP/IP
Named Pipes
... both enabled
Web Config....(for localhost)
<add name="FooData" connectionString="Data Source=localhost\InstanceName;Initial Catalog=DatabaseName;Integrated Security=True;" providerName="System.Data.SqlClient" />
Did have the same problem. Spent like 6 hours when had to migrate some servers.
Tried all suggestions available on this topic and others.
Solution was as simple as server restart!
Very simple solution
use (local)\InstanceName
that's it. it worked for me.
TL;DR; Your SQL Server instance is using dynamic ports which is not working. Force SQL Server to use static port # 1433.
Complete Details: First of all this problem is more likely if you've a mix of default and named instance or named instances only(which was my case).
Key concept: Each instance of Microsoft SQL Server installed on a computer uses a different port to listen for incoming connection requests. Default instance of SQL Server uses port # 1433. As you install named instances then they will start using dynamic ports which is decided at the time of start-up of Windows service corresponding to named SQL Server instance.
My code was failing (with error code 40) to connect to the only named SQL Server instance that I had on my VM. You can try below possible solutions:
Solution # 1: Client code trying to connect to SQL Server instance takes help from SQL Server browser service to figure out port number at which your named instance is listening for incoming connections. Make sure SQL browser service is running on your computer.
Solution # 2: Check the port # (in yellow color) your named SQL Server instance is using from SQL Server configuration manager as shown in the snapshot below:
Use that port number explicitly in your connection string or with sqlcmd shown below:
sqlcmd -s mymachinename,11380 -i deleteDB.sql -o SQLDelete.txt
Solution # 3: Force your named instance to use port # 1433 which is used by default instance. Remember this will work only if you don't have any default SQL Server instance on your computer as the default SQL Server instance would be using using port # 1433 already. Same port number can't be uses by two different Windows services.
Mark TCP Dynamic ports field to blank and TCP Port field to 1433.
Change the port number in your connection string as shown below:
sqlcmd -s mymachinename\instanceName -i deleteDB.sql -o SQLDelete.txt
OR
sqlcmd -s mymachinename,1433 -i deleteDB.sql -o SQLDelete.txt
Note: Every change in TCP/IP settings requires corresponding Windows service restart.
Interestingly enough after resolving the error when I went back to dynamic port setting to reproduce the same error then it didn't happen. Not sure why.
Please read below interesting threads to know more about dynamic ports of SQL Server:
How to configure SQL Server Port on multiple instances?
When is a Dynamic Port “dynamic”?
When to use a TCP dynamic port and when TCP Port?
I got leads to solution of my problem from this blog.
in my case, i had a standalone server, i changed the sql server port default port 1433 in configuration manager to some number and restarted the sql serve service to take effect,i was able to connect to the sql server through management studio if i login to the server. but i was not able to connect from my local machine through sql server, i was getting the error:
A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and
that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server) (Microsoft SQL Server, Error: 5)
I checked and verified all the below
-Named pipes/TCP is enabled.
-Remote connections are allowed.
-Windows Firewall is off
-Created an exception for portin Windows Firewall( this was not necessary in my case as the server is in same subnet network).
-Enabled everything in SQL Server Configuration Manager.
then i chnaged back the port number to default 1433 and restarted the sql server service, and the issue got resolved and i am able to connect the sql server from my local management studio.
I had the same problem. I use the MSSQL Server Management Studio 2017 and solved this problem using these steps:
Check for working fine SQL Server Services services or not.
Also check for working in good condition SQL Server (MSSQLSERVER).
Also check for working fine SQL Server Browser.
Restart SQL Server (MSSQLSERVER)
and fixed it.
You will find most likely your DB name is not correct, you will see the server name in VS like "DESKTOP-0I14BKI" but if you open up SSMS you will see DESKTOP-0I14BKI\SQLBLAHBLAH , simply add "\SQLBLAHBLAH" (instance name) to your "server name" in VS connection properties.
You will see:
To Fix:
Try the following steps:
Open Services window (open "run box" and type services.msc).
Looking for SQL services (with SQL prefix).
Start them (if cannot start. Goto step 4).
Right_click to each service -> Properties -> Change to tab "Log on"-> choise log on as "Local ..." -> 0K. Then start SQL services again.
Try Open SQL and connect database.
In my case,
I opened SQL Server Management Studio and searched for SQLEXPRESS in my Database engine.
It had two instances and I selected the correct one.
If you are working with Asp.net core and using appsettings.json than write server as localhost and after write sql instance name for enabled named pipe like this
"ConnectionString": {
"dewDB": "server=localhost\\dewelopersql;database=dewdb;User ID=sa;password=XXXXX",
},
After following all the steps mentioned here, if it still does not connect, try adding the DNS with the IP address in the hosts file in the etc folder. Adding an IP address instead of DNS name in the connection string should be a temporary solution to check if the connection actually works.
I tried using the local IP address to connect as well as a public one.
I've tried:
Yes, the site can communicate with the server Named pipes/TCP is
enabled. Remote connections are allowed. Windows Firewall is off
Created an exception for port 1433 in Windows Firewall. Enabled
everything in SQL Server Configuration Manager.
i ensured and did the above as well and I just want to share that the DOUBLE BACKSLASH
oBuilder.DataSource = "SPECIFICPCNAME\SQLEXPRESS";
Using a SINGLE BACKSLASH resulted into a build error i.e.: Error 1 Unrecognized escape sequence
I hope this helps the next guy - I've sacrificed dinner, midnight snack and NBA highlights time solving this (shame)
Thanks to [Tamizh venthan]
^_^
Enable TCP/Ip , Piped Protocol by going to Computer Management ->SQL and Services, ensure the Service is On. Enbale the port on the Firewall. Try to login through Command Prompt -> as Admin; last the User Name
should be (local)\SQLEXPRESS. Hope this helps.
Open SQL Server Configuration Manager
Select SQL Server Services from right.
Find your server from right and go to its properties (with right click)
Change log on method to Local System.
I had the same problem and solved the problem by disabling my firewall(ESET).
The first step to solve this problem should be to try pinging your own computer from another computer. If you have firewall on, you may not be able to ping yourself. I tried pinging my own pc, then ping was failed(didnt get response from the server)
I was trying to add a new connection in VS2015. None of the suggestions here worked. Suspecting some sort of a bug in the wizard, especially since SSMS was able to connect just fine, I decided to try and trick it. It worked!
Instead of adding the connection, use "Create new SQL Server Database". Enter your server name and a random name for the new DB, e.g. "test".
Assuming this succeeds, open Server Explorer in VS, locate the connection in Data Connections, right-click it and select Modify Connection.
Change "test" (from step 1) to the name of the existing database you want to connect to. Click "Test Connection". This time it should work!
Delete the temporary database you created in step 1.
I have one more solution, I think.
I recently had changed my computer name so, after I couldn't connect still after trying all above methods.
I changed the Server name..
Server name => (browse for more) => under database engine, a new server was found same as computers new name.
This worked, and life is good again.
I struggled for ages on this one before I realized my error - I had used commas instead of semicolons in the connect string
I had this issue but none of the suggestions above fixed it.
I was seeing this issue when I deployed my website to IIS. The fix was to go into advanced settings against the default app pool and change the identity property from the default to Administrator.
For me it was a Firewall issue.
First you have to add the port (such as 1444 and maybe 1434) but also
C:\Program Files (x86)\Microsoft SQL Server\90\Shared\sqlbrowser.exe
and
%ProgramFiles%\Microsoft SQL Server\MSSQL12.SQLEXPRESS\MSSQL\Binn\SQLAGENT.EXE
The second time I got this issue is when I came back to the firewall, the paths were not correct and I needed to update form 12 to 13! Simply clicking on browse in the Programs and Services tab helped to realise this.
Finally, try running the command
EXEC xp_readerrorlog 0,1,"could not register the Service Principal Name",Null
For me, it returned the error reason
I tried pretty much everything on this page but I had some underlying issues which were actually what needed to be resolved. I was unable to do certain things like open SQL Server Configuration Manager, which ended up being corrupt/missing WMI provider files.
There are lots of tedious ways to resolve this issues according to what I've read, but the tool from tweaking.com was able to remove and replace/repair my WMI (Windows Management Instrumentation) Provider files.
I used to do computer repair and overall the tweaking.com tool really impressed me, and it was suggested from one of the WMI error forum pages I went to.
After I fixed this issue I was able to connect to my SQL db, both locally and remotely.
Hope this helps someone.
open port number 1433 on your server for sql remote connection
If you tried restarting the MSSQLSERVER service, and it did not work, this might be a solution:
If you are using SQLExpress, your server name should be as the following ComputerName\SQLExpress. However, for SQLDeveloper, you do not have to right SQLDeveloper after your ComputerName.

ASP.NET MVC & SQL Server [duplicate]

I can't seem to connect to my database from a site. I get this error:
Named Pipes Provider, error: 40 - Could not open a connection to SQL Server
I tried using the local IP address to connect as well as a public one. I've tried:
Yes, the site can communicate with the server
Named pipes/TCP is enabled.
Remote connections are allowed.
Windows Firewall is off
Created an exception for port 1433 in Windows Firewall.
Enabled everything in SQL Server Configuration Manager.
What else can I do here?
Solving this problem is very easy:
Go to control panel.
search for services.
Open Local services window from your search results
Restart your MSSQLSERVER service.
Screenshot of the steps:
And the simplest solution - check if your slash is back...
I spent about an hour trying to figure out what's wrong with SERVER/INSTANCENAME when everything is configured correctly, named pipes, user access rights... and suddenly it struck me, it's not a slash, it's a backslash (\).
The horror, the shame...
It's a three step process really after installing SQL Server:
Enable Named Pipes
SQL Config Manager --> SQL Server Network Consif --> Protocols --> Named Pipes --> Right-click --> Restart
Restart the server
SQL Config Manager --> SQL Server Services --> SQL Server (SQLEXPRESS) --> Right-click --> Restart
Use proper server and instance names (both are needed!)
Typically this would be .\SQLEXPRESS, for example see the screenshot from QueryExpress connection dialog.
There you have it.
I had just installed SQL SERVER 2012 developer. When I was creating my first SSIS package, I received this pipes error when I was trying to create a data connection task in SQL Server 2012 Data Tools in the Connection Manager box. I resolved with the help of the post above.
If choose a named instance and you call your named instance SSQDatabase1 and your pc's name is PCX1. You must enter PCX1\SSQDatabase1 not just SSQDatabase1
or you will receive the named pipes error.
A thread on MSDN Social, Re: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server, has a pretty decent list of possible issues that are related to your error. You may want to see if any of them could be what you're experiencing.
Incorrect connection string, such as using SqlExpress
Named Pipes(NP) was not enabled on the SQL instance
Remote connection was not enabled
Server not started, or point to not a real server in your connection string
Other reasons such as incorrect security context
try basic connectivity tests between the two machines you are working on
i Just enabled TCP/IP,VIA,Named Pipes in Sql Server Configuration manager , My problem got solved refer this for more info Resolving Named Pipes Error 40
Use SERVER\\ INSTANCE NAME .Using double backslash in my project solved my problem.
Thanks to Damian...
TCP/IP
Named Pipes
... both enabled
Web Config....(for localhost)
<add name="FooData" connectionString="Data Source=localhost\InstanceName;Initial Catalog=DatabaseName;Integrated Security=True;" providerName="System.Data.SqlClient" />
Did have the same problem. Spent like 6 hours when had to migrate some servers.
Tried all suggestions available on this topic and others.
Solution was as simple as server restart!
Very simple solution
use (local)\InstanceName
that's it. it worked for me.
TL;DR; Your SQL Server instance is using dynamic ports which is not working. Force SQL Server to use static port # 1433.
Complete Details: First of all this problem is more likely if you've a mix of default and named instance or named instances only(which was my case).
Key concept: Each instance of Microsoft SQL Server installed on a computer uses a different port to listen for incoming connection requests. Default instance of SQL Server uses port # 1433. As you install named instances then they will start using dynamic ports which is decided at the time of start-up of Windows service corresponding to named SQL Server instance.
My code was failing (with error code 40) to connect to the only named SQL Server instance that I had on my VM. You can try below possible solutions:
Solution # 1: Client code trying to connect to SQL Server instance takes help from SQL Server browser service to figure out port number at which your named instance is listening for incoming connections. Make sure SQL browser service is running on your computer.
Solution # 2: Check the port # (in yellow color) your named SQL Server instance is using from SQL Server configuration manager as shown in the snapshot below:
Use that port number explicitly in your connection string or with sqlcmd shown below:
sqlcmd -s mymachinename,11380 -i deleteDB.sql -o SQLDelete.txt
Solution # 3: Force your named instance to use port # 1433 which is used by default instance. Remember this will work only if you don't have any default SQL Server instance on your computer as the default SQL Server instance would be using using port # 1433 already. Same port number can't be uses by two different Windows services.
Mark TCP Dynamic ports field to blank and TCP Port field to 1433.
Change the port number in your connection string as shown below:
sqlcmd -s mymachinename\instanceName -i deleteDB.sql -o SQLDelete.txt
OR
sqlcmd -s mymachinename,1433 -i deleteDB.sql -o SQLDelete.txt
Note: Every change in TCP/IP settings requires corresponding Windows service restart.
Interestingly enough after resolving the error when I went back to dynamic port setting to reproduce the same error then it didn't happen. Not sure why.
Please read below interesting threads to know more about dynamic ports of SQL Server:
How to configure SQL Server Port on multiple instances?
When is a Dynamic Port “dynamic”?
When to use a TCP dynamic port and when TCP Port?
I got leads to solution of my problem from this blog.
in my case, i had a standalone server, i changed the sql server port default port 1433 in configuration manager to some number and restarted the sql serve service to take effect,i was able to connect to the sql server through management studio if i login to the server. but i was not able to connect from my local machine through sql server, i was getting the error:
A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and
that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server) (Microsoft SQL Server, Error: 5)
I checked and verified all the below
-Named pipes/TCP is enabled.
-Remote connections are allowed.
-Windows Firewall is off
-Created an exception for portin Windows Firewall( this was not necessary in my case as the server is in same subnet network).
-Enabled everything in SQL Server Configuration Manager.
then i chnaged back the port number to default 1433 and restarted the sql server service, and the issue got resolved and i am able to connect the sql server from my local management studio.
I had the same problem. I use the MSSQL Server Management Studio 2017 and solved this problem using these steps:
Check for working fine SQL Server Services services or not.
Also check for working in good condition SQL Server (MSSQLSERVER).
Also check for working fine SQL Server Browser.
Restart SQL Server (MSSQLSERVER)
and fixed it.
You will find most likely your DB name is not correct, you will see the server name in VS like "DESKTOP-0I14BKI" but if you open up SSMS you will see DESKTOP-0I14BKI\SQLBLAHBLAH , simply add "\SQLBLAHBLAH" (instance name) to your "server name" in VS connection properties.
You will see:
To Fix:
Try the following steps:
Open Services window (open "run box" and type services.msc).
Looking for SQL services (with SQL prefix).
Start them (if cannot start. Goto step 4).
Right_click to each service -> Properties -> Change to tab "Log on"-> choise log on as "Local ..." -> 0K. Then start SQL services again.
Try Open SQL and connect database.
In my case,
I opened SQL Server Management Studio and searched for SQLEXPRESS in my Database engine.
It had two instances and I selected the correct one.
If you are working with Asp.net core and using appsettings.json than write server as localhost and after write sql instance name for enabled named pipe like this
"ConnectionString": {
"dewDB": "server=localhost\\dewelopersql;database=dewdb;User ID=sa;password=XXXXX",
},
After following all the steps mentioned here, if it still does not connect, try adding the DNS with the IP address in the hosts file in the etc folder. Adding an IP address instead of DNS name in the connection string should be a temporary solution to check if the connection actually works.
I tried using the local IP address to connect as well as a public one.
I've tried:
Yes, the site can communicate with the server Named pipes/TCP is
enabled. Remote connections are allowed. Windows Firewall is off
Created an exception for port 1433 in Windows Firewall. Enabled
everything in SQL Server Configuration Manager.
i ensured and did the above as well and I just want to share that the DOUBLE BACKSLASH
oBuilder.DataSource = "SPECIFICPCNAME\SQLEXPRESS";
Using a SINGLE BACKSLASH resulted into a build error i.e.: Error 1 Unrecognized escape sequence
I hope this helps the next guy - I've sacrificed dinner, midnight snack and NBA highlights time solving this (shame)
Thanks to [Tamizh venthan]
^_^
Enable TCP/Ip , Piped Protocol by going to Computer Management ->SQL and Services, ensure the Service is On. Enbale the port on the Firewall. Try to login through Command Prompt -> as Admin; last the User Name
should be (local)\SQLEXPRESS. Hope this helps.
Open SQL Server Configuration Manager
Select SQL Server Services from right.
Find your server from right and go to its properties (with right click)
Change log on method to Local System.
I had the same problem and solved the problem by disabling my firewall(ESET).
The first step to solve this problem should be to try pinging your own computer from another computer. If you have firewall on, you may not be able to ping yourself. I tried pinging my own pc, then ping was failed(didnt get response from the server)
I was trying to add a new connection in VS2015. None of the suggestions here worked. Suspecting some sort of a bug in the wizard, especially since SSMS was able to connect just fine, I decided to try and trick it. It worked!
Instead of adding the connection, use "Create new SQL Server Database". Enter your server name and a random name for the new DB, e.g. "test".
Assuming this succeeds, open Server Explorer in VS, locate the connection in Data Connections, right-click it and select Modify Connection.
Change "test" (from step 1) to the name of the existing database you want to connect to. Click "Test Connection". This time it should work!
Delete the temporary database you created in step 1.
I have one more solution, I think.
I recently had changed my computer name so, after I couldn't connect still after trying all above methods.
I changed the Server name..
Server name => (browse for more) => under database engine, a new server was found same as computers new name.
This worked, and life is good again.
I struggled for ages on this one before I realized my error - I had used commas instead of semicolons in the connect string
I had this issue but none of the suggestions above fixed it.
I was seeing this issue when I deployed my website to IIS. The fix was to go into advanced settings against the default app pool and change the identity property from the default to Administrator.
For me it was a Firewall issue.
First you have to add the port (such as 1444 and maybe 1434) but also
C:\Program Files (x86)\Microsoft SQL Server\90\Shared\sqlbrowser.exe
and
%ProgramFiles%\Microsoft SQL Server\MSSQL12.SQLEXPRESS\MSSQL\Binn\SQLAGENT.EXE
The second time I got this issue is when I came back to the firewall, the paths were not correct and I needed to update form 12 to 13! Simply clicking on browse in the Programs and Services tab helped to realise this.
Finally, try running the command
EXEC xp_readerrorlog 0,1,"could not register the Service Principal Name",Null
For me, it returned the error reason
I tried pretty much everything on this page but I had some underlying issues which were actually what needed to be resolved. I was unable to do certain things like open SQL Server Configuration Manager, which ended up being corrupt/missing WMI provider files.
There are lots of tedious ways to resolve this issues according to what I've read, but the tool from tweaking.com was able to remove and replace/repair my WMI (Windows Management Instrumentation) Provider files.
I used to do computer repair and overall the tweaking.com tool really impressed me, and it was suggested from one of the WMI error forum pages I went to.
After I fixed this issue I was able to connect to my SQL db, both locally and remotely.
Hope this helps someone.
open port number 1433 on your server for sql remote connection
If you tried restarting the MSSQLSERVER service, and it did not work, this might be a solution:
If you are using SQLExpress, your server name should be as the following ComputerName\SQLExpress. However, for SQLDeveloper, you do not have to right SQLDeveloper after your ComputerName.

Can someone explain why after installing SQL Server some PC gets suffix "\SQLEXPRESS" and some don't?

Can someone explain why after installation of SQL Server some PC get a suffix of \SQLEXPRESS and some don't? Is there an option to change it?
Any suggestions or tips would be appreciated.
That is the SQL Server instance name for the new SQL Server you installed. A single machine can host multiple instances of SQL Server. The naming convention you see: hostname\instance_name is used to identify the different SQL Server instances running on a single machine.
When you install SQL Server Express, the default instance name created is SQLEXPRESS.
See:
Default instance name of SQL Server Express
How to: Identify a SQL Server Express Instance
Instance Configuration
The hostname is used for machine to machine networking. That is the same name that is used for Netbios/SMB file sharing services (\\hostname) and normally resolved for TCP/IP services through DNS (http://hostname).
The hostname\instance_name is purely a SQL server naming convention. Its only purpose is to identify a running instance of SQL server. The SQL server client network libraries know how to resolve these instance names. The standard network stacks do not. This means the following do not work:
ping hostname\instance_name
\hostname\instance_name
http://hostname\instance_name
The \instance_name only works with SQL server network clients.

Configure a SQL Server Instance as (local)

Each member of our development team has a copy of our application's database running on a local version of SQL Server 2008 Enterprise with SP1. Everyone is able to access the database by specifying their server and instance name in their web.config file, but to best share the developer version of our web.config file, we have standardized on making connections strings generic by using integrated security and setting server property to (local). This strategy is working fine for the majority of our 64-bit Windows 7 machines but in few cases (local) isn't recognized. We have compared settings via the SQL Server Configuration Manager (namely ensuring that the named pipes protocol was enabled) and we've tried setting the "(local)" alias via SQL Server Client Network Utility, but we haven't any luck. What needs to be done in order to use (local) in our connections strings?
Trying changing the Pipe Name for your instance to "\.\pipe\sql\query".
You can find that setting by starting SQL Server Configuration Manager, and navigating to SQL Server Network Configuration > Protocols for (Instance Name) and right-clicking on Named Pipes and selecting Properties. If Named Pipes is not enabled, be sure to enable it before restarting the SQL Server service (see comment by #NoahHeldman).
When connecting to the default instance (that is, without an instance name), SQL Server uses the default port of 1433 and the default pipe name of "\.\pipe\sql\query". Changing it back to match should (hopefully) fix it.
Those machines where the database connection as (local) doesn't work is probably that way because during the database installation, the instance name was set to something specific, rather than the default of "default instance". You can change these instance names, which may resolve this issue: http://coderjournal.com/2008/02/how-to-change-instance-name-of-sql-server/.
I think this occurs when you have SQL Server Express already installed and running, and then install SQL Server Developer Edition / Standard / etc....not 100% sure though, but from what I recall, that may be the case.

JDBC connect string for SQL Server cluster

I need to setup a JDBC connection string to SQL Server.
This question is similar to the the C# ADO.Net connection question. This one is specific to JDBC connection strings.
The usual format for the JDBC string is "jdbc:sqlserver://{host}:{port}".
Now, for a SQL server cluster I have a cluster name vvv\iii ({virtual server}{instance name}).
There's no problem setting up an ODBC connection through the "New Data Source to SQL Server" wizard when using the vvv\iii string as the server name. However it seems the JDBC connection string requires a specific host and port.
Is there a way to make a JDBC connect string to a SQL Server cluster?
it turns out that you can use the "instanceName" property within the JDBC string, as documented on the Microsoft Technet page in section "Named and Multiple SQL Server Instances". What worked in my case was the following string for virtual server vvv and database instance name iii:
"jdbc:sqlserver://vvv;instanceName=iii"
When using a SQL Server named instance in a cluster or stand alone environment each SQL Server instance is dynamically assigned a port number on startup. The SQL Server Browser server handles requests to each instance because each server restart could change the port number used by each instance. The first instance to start on a server reboot gets assigned 1433 but there is no guarantee if you have 2 instances that one of them will always get 1433. There are several veriables that affect the startup and recovery time it takes for an instance to start. This can change each time.
That being sad... when connecting to a named instance the jdbc connection string should look like this:
jdbc:sqlserver://server_name/db_name;instance=instance_name
rather than this
jdbc:sqlserver://server_name:1433/db_name;instance=instance_name
note that the default database "/db_name" is optional. If exclued the connection will use the default database assigned to the SQL Server login.
The cluster resource has a host name and a listening port. Use jdbc:sqlserver://{virtualserver}:1433 (or the appropriate listening port if not listening on the default one).
I'd comment Mark Stewart's remark, but the reputation is lacking. My source doesn't mention /db_name and I can't get it to work either. Maybe another case of confused instance names?
Make sure you leave the port definition off as the cluster determine this for you.
So my datasource definition looks like:
jdbc:sqlserver://sqlcluster_hostname\instancename;DATABASENAME=databasename;sendStringParametersAsUnicode=false;SelectMethod=direct
I ran into this issue while trying to setup a Railo datasource to connect to MSSQL cluster.
Slightly off topic ... The standard Railo datasource MSSQL driver option sets the port to "-1" if you leave the port field empty however if you set it to "0" then it removes the port definition altogether and then everything works. But the best way is to choose 'Other - JDBC Driver' to define the JDBC connection string in full as above.

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