Whenever possible, you should use:
EXEC sp_executesql @sql [rather than EXEC(@sql)]
because it is far less susceptible to SQL injection, although not foolproof depending on what you are trying to make dynamic.
If you just need to have a stored proc run in the context of a given db, you can do that far more effectively by:
1) prefixing the proc name with sp_
2) creating the proc in the master db
3) setting the proc as a "system object"
Then you can use it from any db and it functions within the context of that db.
SQL DBA,SQL Server MVP(07, 08, 09) "It's a dog-eat-dog world, and I'm wearing Milk-Bone underwear." "Norm", on "Cheers". Also from "Cheers", from "Carla": "You need to know 3 things about Tortelli men: Tortelli men draw women like flies; Tortelli men treat women like flies; Tortelli men's brains are in their flies".