User-defined functions in SQL

User defined functions are stored subprograms that must return a value with return statements. User defined functions are classified functions.

• Scalar function: This are the user defined functions that return a single value. 

• Valued functions: This are user defined functions that returns a table.  Table valued functions are classified into inline table valued functions and multistatement table values statement.

• Inline Table valued functions:This are the table valued functions that contain a single statement i.e the return statement with a select statement within it, whose results will be converted inline as a table.

Inline table valued function must not contain the keyword begin and end.

• Multistatement valued functions: This are table value functions that contain multiple statements. In case of multistatemnet table values function you have to create a table in a function manual, insert rows into it and return it manual.