Why can't I use "create schema" in a begin/end block in SQL Management Studio?

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

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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).

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最佳答案

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

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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

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Here is an even simpler solution (simpler check):

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

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Sometimes (always) you're not allowed to use Dynamic SQL, so using EXEC is not the best approach. Using GO statement can do things better:

USE [MyDB]
GO


IF (SCHEMA_ID('MySchema') IS NOT NULL)
BEGIN
DROP SCHEMA [MySchema];
END


GO


CREATE SCHEMA [MySchema] AUTHORIZATION [dbo]


GO