running a query from C# on sql server

when i run a query like this:

    SqlDataAdapter da开发者_如何学JAVAp = new SqlDataAdapter("select * from some table", myConnection);

before doing the select, should i be doing "use somedatabase; go" ??

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No, your database and schema should be set in the connection string for myConnection.

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No you should specify the database name in myConnection

InitialCatalog = [databaseName] 

Your connection string should something look like this

data source=[ServerName];Integrated Security=SSPI;Persist Security Info=False;Initial Catalog=[DatabaseName];

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I imagine myConnection is already specifying a default catalog (i.e. database) in its connection string, so you don't need to use the use line.

See here for details.

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No; the myConnection object's connection string should define which database needs to be used, along with the server and login information.

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That should all be in the myConnection variable, since I presume that contains the connection string.

Although you might want to call using on the DataAdapter

using(SqlDataAdapter dap = new SqlDataAdapter("select * from some table", myConnection)
{
    //do stuff with dap here 
}//dispose of dap

Since it does inherit from something that implements IDisposable.

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Your connection string tells it what database to connect to.

connectionString = "Data Source=SERVERNAME; Initial Catalog=DATABASENAME; Integrated Security=SSPI;";

That would create a connection to a server and database using windows authentication.