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System Functions SQL Server provides many system functions that you can use to perform a variety of operations. They cannot be modified. Transact-SQL errors that cause a statement to be canceled and continue with the next statement in the module such as triggers or stored procedures are treated differently inside a function.
In functions, such errors cause the execution of the function to stop. This in turn causes the statement that invoked the function to be canceled. END block cannot have any side effects. Function side effects are any permanent changes to the state of a resource that has a scope outside the function such as a modification to a database table. The only changes that can be made by the statements in the function are changes to objects local to the function, such as local cursors or variables.
Modifications to database tables, operations on cursors that are not local to the function, sending e-mail, attempting a catalog modification, and generating a result set that is returned to the user are examples of actions that cannot be performed in a function.
However, SQL Server does not execute the function when it is invoked. The number of times that a function specified in a query is actually executed can vary between execution plans built by the optimizer. The number of times the subquery and its function is executed can vary with different access paths chosen by the optimizer.
For more information and performance considerations on user-defined functions, see Create User-defined Functions Database Engine.
Assignments of values to objects local to the function, such as using SET to assign values to scalar and table local variables. Cursor operations that reference local cursors that are declared, opened, closed, and deallocated in the function. FETCH statements that return data to the client are not allowed. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Sql Server deterministic user-defined function Ask Question. Asked 11 years, 1 month ago. Active 3 years, 6 months ago.
Viewed 19k times. I have the following user-defined function: create function [dbo]. Improve this question. Add a comment. Active Oldest Votes. The one you posted isn't. That is the only thing that matters to sql server and this function will never be derministic because it references a table. From booksonline: quote: User-Defined Function Determinism Whether a user-defined function is deterministic or nondeterministic depends on how the function is coded. User-defined functions are deterministic if: The function is schema-bound.
All built-in or user-defined functions called by the user-defined function are deterministic. The body of the function references no database objects outside the scope of the function. For example, a deterministic function cannot reference tables other than table variables that are local to the function. The function does not call any extended stored procedures. User-defined functions that do not meet these criteria are marked as nondeterministic. Built-in nondeterministic functions are not allowed in the body of user-defined functions.
EDIT: if you pass in the address components rather than an ID and use schemabinding, etc it will work. But it does mean that you could create real problems for yourself if you are not careful about your use of this keyword. Why should it matter? Because under certain circumstances such as the one identified by the developer above , Oracle Database will not execute your function, but instead simply use a previously cached return value.
Within the scope of a single server call e. If in that same server call, you pass the same input values to the function, the database engine may choose to not actually execute the function, but instead simply pass back the previously-computed return value for those same inputs. That's why this developer saw such a great leap forward in performance.
When and if that same query is run again, the engine will start rebuilding and using that cache. While that statement executing, though, no matter what sort of changes are made to the table, no matter if a commit is issued or not, those changes will not be visible to the statement that called the function.
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