Develop Reference

Cannot connect to SQL Server using SqlClient in a desktop application

Connecting to SQL Server with a SQL username and password is no problem at all.
These scenarios work just fine:
from C# code using SqlClient in ASP.NET / MVC
with ssms
with Visual Studio Connection Properties Wizard
For example, this works in an MVC project:
new SqlConnection("Server=DB1;Database=testdb;User Id=testuser;Password=testuser1;").Open();
But this identical code fails when run in a desktop application project. It causes the following inner exception error:
user name or password is incorrect
(yes there is a space between user and name)
I've tried:
making sure the protocols are right in SQL Config Manager.
opening up ports in the firewall on client and server.
connecting to another database to see if it's the database and not the client.
the NuGet version of SqlClient.
restarting the dev machine and the server.
ensured the Browser SQL service is running.
ensured the main SQL service is set to automatic and is running.
SqlClient, OLEDB, and ODBC along with appropriate connection strings.
Storing the username and password in a separate credentials object.
Specifying Integrated Security=False in the connection string
But still, nothing.
Why can I connect to SQL Server from everything except from code running in a desktop .NET application? Is something along the way stripping my password out before the connection happens?

Let's try :
data source=DB1;initial catalog=testdb;persist security info=True;user id=testuser;password=testuser1;
User must be a SQL user.

VS application can't connect to database after attaching it in SSMS

I have a windows form application (developed in VS Express 2013) that connects through an instance of SQL Server 2012 to a database. Both the application and database are on my local system; I just needed a GUI to more easily interface with this very large database that stores my research data. When I initially compile and deploy the application, it works fine and has no connection problems with the database. However, if I then attach the database in SQL Server Management Studio (which I sometimes want to do) I get an error the next time I try to use the application - "Cannot open database ..... requested by the login, the login failed". I get this error even if I take the database offline and detach it before quitting SSMS. And just to be clear - I'm not making any changes to the database in SSMS, I'm just looking at the data. The connection string used by VS is Data Source (LocalDB)\v11.0;AttachDbFilename=|DataDirectory|\CollectionMetricsDatabase.mdf;Integrated Security=True.
Any idea what the problem is?

Maybe the instance of SQL Server 2012 has a max number of concurrent connections and you exceed that with your two connections at once (SSMS connection and application's connection). Check the settings in SSMS.
Another thing to try - Based on your connection string, you are using Integrated Security, which in my experience means the application connects using Windows credentials. That can be fragile, because it means that whatever 'user' runs the application (if hosted in IIS, this will be the App Pool user) is the one whose Windows credentials are used. I would suggest creating a SQL login user (in SSMS) for the database, with db_owner access, and then changing the application's connection to be username/password based instead. You may need to enable Mixed Authentication for the SQL Server instance in SSMS if it doesn't already allow it.

You need to connect in SSMS with the localDB connection string. Attaching it will prevent it from working with localDB.
In SSMS, create a connection to (LocalDB)\v11.0. You should see your DB there already.

The problem is that you are connecting to the database file directly not through SQL Server.
Only one user can have a lock on the file at the time.
You need to recreate a connection string for your app.
That is why you were needing to detach the database.
Since this is only a personal project you could live with things as they are, at least you know the server is only running when you need it.
create connection msdn

ASP.NET SqlException when publishing in IIS Web Server

I've just start working on an ASP.NET Web Application in Visual Studio 2015 and SQL Server 2014. Somewhere, I need to connect to my local database and I use this:
ConnStr = "Data Source=(localdb)\\MSSQLLocalDB;Initial Catalog=my_db;Integrated Security=True";
It works fine when I run the application through VS in my browser. I can access the db and do whatever I want to do. But, when I publish my application in IIS Web Server, and then I open it in browser, it still works OK until I have to access the db. At that moment it throws SqlException:
System.Data.SqlClient.SqlException: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. .
Maybe it is a server name problem and I should use an IP and a Port instead of that name, but I'm not sure because I don't have experience on this.

You are correct: You should use server name and/or IP in your connection string.
Using something like "local" or "localhost" means that your code is not portable. Another option would be to store your connection strings in two separate config files - one for your local copy (for development and troubleshooting) and one for your server (for portability). I have two config files in my solutions:
Web.config
WebServer.config
Then, when I deploy to the server, I just delete Web.config and rename WebServer.config to Web.config. It's totally portable and you'll never have connection string troubles again!
Also noteworthy: you're not including credentials in your connection string, which means that you're using windows authentication when connecting to SQL server. When debugging through visual studio, the application will run as you - and if you have the needed permissions, it will work. However, when running in IIS, it won't be running as you (at least, it SHOULDN'T be) - so you could run into issues there, as well.
EDIT
This link might be useful for you: https://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlconnection.connectionstring.aspx
Your connection string should look like this:
Data Source=192.168.1.10,1433;Initial Catalog=YourDatabaseName;User ID=SqlUserName;Password=SqlPassword;Connection Timeout=60; Max Pool Size=3000;
(you can set max pool size and connection timeout to whatever you want - or omit them entirely.
Also, regarding your windows issues - you need to make sure that the windows account IIS is using has permissions to traverse your network and reach your SQL Server instance. That said, I suggest that you use a SQL account instead of windows authentication.

Since you are using integrated security in connection string you will have to modify the Identity of App pool under which your application is running.
The Identity will be your windows username and password.
To change the username and password you need to go the advance settings of the app pool and process model you can see identity where you can add your windows credentials
Hope this helps

There are two problems in you connection string:
"Integrated Security" means you are using the native windows system for authentication. Similar to opening SSMS on the database using your Windows password. IIS is now trying to connect to the database, and connection string is telling to use the process that IIS is running under.
You can create a non-windows user in SQL Server and put the credentials into the connection string. Or you can grant the IIS user DB privileges. Or you can a lot different things here, but theses are the easiest to get you moving.
THe second problem in the connection string is the data source. Is there SQL Server on you local machine? If so that's why it's not working. Try to run your app in VS but against the remote SQL Server. That should be your next step.

The problem was that I thought that SQL Server was installed automatically with VS or at least with SQL Server Management Studio. BUT NO. So, as far as I understand, till know I have not worked with a real SQL Server. When I checked SQL Server Configuration Manager there were nothing running at SQL Server Services and so I realized that I was missing something.
Then, I installed SQL Server Express and build my db there. Now it is working fine even when I publish it. The connection string is
Data Source=.\\SQLEXPRESS;Initial Catalog=my_db;User ID=username;Password=pass
It can also be:
Data Source=localhost\\SQLEXPRESS;Initial Catalog=my_db;User ID=username;Password=pass

Installing C# Windows Form Application with Database on another system

I have developed a winform application in C#.net and using SQL Server 2008.
My application inserts and updates values into database.
Is it possible to install the application on a another system which doesn't have sql server on it?

Imagine using sql azure. Cloud based sql server. The database is never on the same physically computer. It's all down to the connection string.
With an on premise database you need to make sure the database allows external connections, maybe opening up firewall etc. then make sure the connection string is set correctly on the application to talk to external database.
You can even configure to change the connection string as required pointing at different databases depending on the individual requirements.
Scott

Yes, you can. You can access the DB remotely by referring remote DB server in connection string.

It is possible, if you are looking to run the application on machine that is running on the same Domain as the SQL Server and has privileges to the SQL Server.

C# application accessing remote sql server 2008 instance ... not working

I have a console app that needs to connect to a remote sql server 2008 instance....
this particular line throws an error even though i have access to that database...
connection.open() is the line that is throwing the error...

Make sure that Sql server 2008 instance available at your system where you are running your application.
Atleast client version of Sql server 2008 should be installed on development machine.
Check connection string and server system also allow network connection.

Make sure the connection string in you console app uses the same credentials and settings that you use to successfully connect in management studio.
Are you using Windows authentication in one place and a SQL login in another?

Have you been able to connect to this remote server before? If you have been able to connect previously, but cannot do so now, that may be an indication that a backup copy of the database, from another server, has been restored to that server.
When you write that you "have access" to that database, how do you connect? Close your copy of SQL Server Management Studio and re-open it; when you get the Connect dialog, be sure to enter the user credentials that your console app uses to connect. Do you see your database? Are you able to execute stored procedures, run SELECT statements, or otherwise do what you would expect?
If you do not see the database--or if you cannot do the activities you expect, you have probably restored a database from another server. This is very common--a database developer is working on the next revision of the database on his development machine; when it comes time to deploy he backs up the database, copies it to the server, and restores the database. Now he can't connect--and can't understand why.
The reason is that the Login and User are presented in the SSMS UI as strings--but in fact they are integer IDs. You will have to do a bit of scripting to delete the invalid User record from the database in order to assign it to the new server's Login.
If this sounds like your problem, respond--I'll check back in a bit, and follow up with more help.
JM