怎样用变量作为数据库名？

[beizijing]

怎样用变量作为数据库名？
declare @dname sysname
set @dname='testDB'
set @dname=' select * from @testDB.dbo.sysprotects'
exec sp_executesql @dname

[newnewworm]

declare @dbname nvarchar(20)
@SQLString nvarchar(500)
set @dname=N'testDB.dbo.sysprotects'
set @SQLString= N'select * from '+ @dname
exec sp_executesql @SQLString

[txlicenhe]

declare @dname sysname
set @dname='testDB'
set @dname=' select * from '+@dname+'.dbo.sysprotects'
exec(@dname)

[zlz7803]

declare @dname varchar(50)
declare @sql varchar(500)
set @dname='testDB'
set @dname=rtrim(@dname)+'.dbo.sysprotects'
set @sql =' select * from '+ @dname
exec (@sql)

[lansquenet]

都说完了,无话可说

[perfwell]

declare @dbname nvarchar(20)
@SQLString nvarchar(500)
set @dname=N'testDB.dbo.sysprotects'
set @SQLString= N'select * from '+ @dname
exec sp_executesql @SQLString