Why can't I use “create schema” in a begin/end

问题:

I generated a script which creates all users and schemas for this database and when I wrap the CREATE statements with an IF EXISTS check I find that it does not allow the CREATE SCHEMA call to run in the BEGIN/END block. It complains that it is invalid syntax. Yet I can run the command on it's own. A sample of the code is below. I am using SQL Server 2008 and Management Studio R2. Why is this invalid syntax?

--DROP SCHEMA [acme]

IF (NOT EXISTS (SELECT * FROM sys.schemas WHERE name = 'acme')) 
BEGIN
    CREATE SCHEMA [acme] AUTHORIZATION [dbo]
END

回答1:

Schema creations must be the only statement in a batch. One way to get around it is like so:

IF (NOT EXISTS (SELECT * FROM sys.schemas WHERE name = 'acme')) 
BEGIN
    EXEC ('CREATE SCHEMA [acme] AUTHORIZATION [dbo]')
END

回答2:

Here is an even simpler solution (simpler check):

IF (SCHEMA_ID('acme') IS NULL) 
BEGIN
    EXEC ('CREATE SCHEMA [acme] AUTHORIZATION [dbo]')
END

回答3:

It needs to be in its own batch. You can wrap it in EXEC('')

EXEC('CREATE SCHEMA [acme] AUTHORIZATION [dbo]')

I believe the reason for the requirement is something to do with an older version of the CREATE SCHEMA syntax introduced in version 6.5 (at least that's what it says here).

回答4:

CREATE SCHEMA must be in it's own batch, so embed it inside an EXEC and you should be OK.

IF (NOT EXISTS (SELECT * FROM sys.schemas WHERE name = 'acme')) 
BEGIN
    EXEC ('CREATE SCHEMA [acme] AUTHORIZATION [dbo]')
END