SQL Server: Table-valued Functions vs. Stored Procedures
I have been doing a lot of reading up on execution plans and the problems of dynamic parameters in stored procedures. I know the suggested solutions for this.
My question, though, is everything I have read indicated that SQL Server caches the execution plan for stored procedures. No mention is made of Table-value functions. I assume it does so for Views (out of interest).
Does it recompile each time a Table-value function is called?
When is it best to use a Table-value function as opposed to a stored procedure?
Answer
An inline table valued function (TVF) is like a macro: it's expanded into the outer query. It has no plan as such: the calling SQL has a plan.
A multi-statement TVF has a plan (will find a reference).
TVFs are useful where you want to vary the SELECT list for a parameterised input. Inline TVFs are expanded and the outer select/where will be considered by the optimiser. For multi-statement TVFs optimisation is not really possible because it must run to completion, then filter.
Personally, I'd use a stored proc over a multi-statement TVF. They are more flexible (eg hints, can change state, SET NOCOUNT ON, SET XACTABORT etc).
I have no objection to inline TVFs but don't tend to use them for client facing code because of the inability to use SET and change state.