How to use a variable to specify filegroup in SQL Server

Question

I want to alter a table to add a constraint during upgrade on a SQL Server database.

This table is normally indexed on a filegroup called 'MY_INDEX' - but may also be on a database without this filegroup. In this case I want the indexing to be done on the 'PRIMARY' filegroup.

I tried the following code to achieve this:

DECLARE @fgName AS VARCHAR(10)

SET @fgName = CASE WHEN EXISTS(SELECT groupname
                                FROM sysfilegroups
                                WHERE groupname = 'MY_INDEX')
                    THEN QUOTENAME('MY_INDEX')
                    ELSE QUOTENAME('PRIMARY')
              END

ALTER TABLE [dbo].[mytable]
ADD CONSTRAINT [PK_mytable] PRIMARY KEY
(
    [myGuid] ASC
)
ON @fgName -- fails: 'incorrect syntax'

However, the last line fails as it appears a filegroup cannot be specified by variable.

Is this possible?

Answer 1

I've found that dynamic sql works when passing variables in DDL statements.

Try something like this:

DECLARE @fgName AS VARCHAR(10) 

SET @fgName = CASE WHEN EXISTS(SELECT groupname 
                                FROM sysfilegroups 
                                WHERE groupname = 'MY_INDEX') 
                    THEN QUOTENAME('MY_INDEX') 
                    ELSE QUOTENAME('PRIMARY') 
              END 

DECLARE @sql as varchar(1024)

SET @sql = 'ALTER TABLE [dbo].[mytable] ADD CONSTRAINT [PK_mytable] PRIMARY KEY ( 
    [myGuid] ASC ) ON ' + @fgName

EXEC(@sql)

I hope that helps....