Summary of methods for udfs in sqlserver

"User-defined functions" are common statements, while "user-defined functions" are written in SQL Server.

SQL Server 2000 allows users to create user-defined functions. User-defined functions can return values.

User-Defined Functions are classified into scalar functions or table-valued functions.

If the RETURNS clause specifies a scalar data type, the function is a scalar value function. You can use multiple Transact-SQL statements to define scalar value functions.
If the RETURNS clause specifies a TABLE, the function is a TABLE value function.
Table valued functions can also be divided into: Embedded table valued functions (intra-row functions) or multi-statement Functions

If the TABLE specified by the RETURNS clause does not contain a list of columns, this function is an embedded TABLE value function.
If the TABLE type specified by the RETURNS clause contains columns and their data types, this function is a multi-statement TABLE value function.
Scalar function example
Copy codeThe Code is as follows:
Create function dbo. Foo ()
RETURNS int
AS
BEGIN
Declare @ n int
Select @ n = 3
Return @ n
END

Nested table value function example
Copy codeThe Code is as follows:
Create function dbo. Foo ()
RETURNS TABLE
AS
Return select id, title from msgs

The nested table value function has only one select statement.

Multi-statement Table value function example (Part)
Copy codeThe Code is as follows:
Create function fn_FindReports (@ InEmpId nchar (5 ))
RETURNS @ retFindReports TABLE (empid nchar (5) primary key,
Empname nvarchar (50) not null,
Mgrid nchar (5 ),
Title nvarchar (30 ))
...

Pay attention to its RETURNS section.

The following statements can be used in the body of a Multi-statement function. Statements not listed in the following list cannot be used in the function body.

Value assignment statement.
Control Flow statement.
DECLARE statement, which defines the local data variables and cursors of the function.
SELECT statement, which contains a selection list with an expression. The expression in the list grants the value to the local variable of the function.
A cursor operation that references a local cursor declared, opened, closed, and released in a function. Only FETCH statements that assign values to local variables using the INTO clause are allowed. FETCH statements that return data to the client are not allowed.
INSERT, UPDATE, and DELETE statements. These statements modify the local table variables of the function.
EXECUTE statements call extended stored procedures.