DECLARE @current_bind varchar(30)
SET @current_bind = 'tempdb_large_01'
DECLARE @set_tempdb varchar(30)
SET @set_tempdb = 'blub'

CASE WHEN @current_bind='tempdb_large_01' then SET @set_tempdb = 'tempdb_large_02'
			WHEN @current_bind='tempdb_large_02' then SET @set_tempdb = 'tempdb_large_03'
			WHEN @current_bind='tempdb_large_03' then SET @set_tempdb = 'tempdb_large_01'
		ELSE SET @set_tempdb = 'blub'
		END

print 'current: %1! - set: %2!', @current_bind, @set_tempdb
go
DECLARE @current_bind varchar(30)
SET @current_bind = 'tempdb_large_01'
DECLARE @set_tempdb varchar(30)
SET @set_tempdb = 'blub'

IF @current_bind='tempdb_large_01' BEGIN SET @set_tempdb = 'tempdb_large_02' END
IF @current_bind='tempdb_large_02' BEGIN SET @set_tempdb = 'tempdb_large_03' END
IF @current_bind='tempdb_large_03' BEGIN SET @set_tempdb = 'tempdb_large_01' END

print 'current: %1! - set: %2!', @current_bind, @set_tempdb
go