t-SQL USE关键字问题

Question

Say, I just created a database, then created a login and and now I need to assign a user to it. So I do:

CREATE DATABASE [testdb2] COLLATE SQL_Latin1_General_CP1_CI_AS;
CREATE LOGIN testusr1 WITH PASSWORD = 'mystrongpassword';
USE [testdb2];
CREATE USER testusr1 FOR LOGIN testusr1;

But the USE line returns this error:

Database 'testdb2' does not exist. Make sure that the name is entered correctly.

Answer 1

Add some GO commands:

Signals the end of a batch of Transact-SQL statements to the SQL Server utilities.

Eg,

CREATE DATABASE [testdb2] COLLATE SQL_Latin1_General_CP1_CI_AS;
GO
CREATE LOGIN testusr1 WITH PASSWORD = 'mystrongpassword';
GO
USE [testdb2];
GO
CREATE USER testusr1 FOR LOGIN testusr1;

GO is not a Transact-SQL statement; it is a command recognized by the sqlcmd and osql utilities and SQL Server Management Studio Code editor. SQL Server utilities interpret GO as a signal that they should send the current batch of Transact-SQL statements to an instance of SQL Server. The current batch of statements is composed of all statements entered since the last GO, or since the start of the ad hoc session or script if this is the first GO. A Transact-SQL statement cannot occupy the same line as a GO command. However, the line can contain comments. Users must follow the rules for batches. For example, any execution of a stored procedure after the first statement in a batch must include the EXECUTE keyword. The scope of local (user-defined) variables is limited to a batch, and cannot be referenced after a GO command.

Answer 2

You have to use GO after your CREATE DATABASE statement, and also after your CREATE LOGIN statement.
GO is used as a batch separator. You can changed this if you want to use something else as a batch separator instead of GO. Go to Tools -> Options -> Query Execution, and see the Batch Separator section.
GO can also be used with an int parameter for example:

INSERT INTO #tmp
SELECT 1, 2, 3
GO 10

Which will insert the values into #tmp 10 times.