Difference between Stored Procedure and User Defined Functions

Stored procedure :

A stored procedure is a program (or procedure) which is physically stored within a database. They are usually written in a proprietary database language like PL/SQL for Oracle database or PL/PgSQL for PostgreSQL. The advantage of a stored procedure is that when it is run, in response to a user request, it is run directly by the database engine, which usually runs on a separate database server. As such, it has direct access to the data it needs to manipulate and only needs to send its results back to the user, doing away with the overhead of communicating large amounts of data back and forth.

CREATE PROCEDURE dbo.<StoredProcedureName>
/*
(
@<parameter1> datatype = default value,
@<parameter2> datatype OUTPUT
)
*/
AS
/* SET NOCOUNT ON */
RETURN

User-defined function :

A user-defined function is a routine that encapsulates useful logic for use in other queries. While views are limited to a single SELECT statement, user-defined functions can have multiple SELECT statements and provide more powerful logic than is possible with views.


CREATE FUNCTION dbo.<FunctionName>
(
/*
@<parameter1> datatype = default value,
@<parameter2> datatype
*/
)
RETURNS /* datatype */
AS
BEGIN
/* sql statement ... */
RETURN /* value */
END

• Procedure can return zero or n values whereas function can return one value which is mandatory.
• Procedures can have input,output parameters for it whereas functions can have only input parameters.
• Procedure allow select as well as DML statement in it whereas function allow only select statement in it.
• Functions can be called from procedure whereas procedures cannot be called from function.
  
• Exception can be handled by try-catch block in a procedure whereas try-catch block cannot be used in a function.
• We can go for transaction management in procedure whereas we can't go in function.
• Procedures can not be utilized in a select statement whereas function can be embedded in a select statement.