Function can be used in an expression but we cann't use
procedure in an expression

Difference between function and stored proc:
========================================================

Stored Procedure :supports deffered name resoultion Example 
while writing a stored procedure 

that uses table named tabl1 and tabl2 etc..but actually not 
exists in database is allowed 

only in during creation but runtime throws errorFunction 
wont support deffered name 

resolution. 
2. Stored procedure returns always integer value by default 
zero. where as function return 

type could be scalar or table or table values(SQL Server).
3. Stored Procedure is pre compiled exuction plan where as 
functions are not.
4. Stored Procedure retuns more than one value at a time 
while funtion returns only one 

value at a time.
5. We can call the functions in sql statements (select max
(sal) from emp). where as sp is 

not so
6. Function do not return the images,text whereas sp 
returns all.
7. Function and sp both can return the values. But function 
returns 1 value only.
procedure can return multiple values(max. 1024) we can 
select the fields from function. in 

the case of procdure we cannot select the fields.
8. Functions are used for computations where as procedures 
can be used for performing 

business logic
9. Functions MUST return a value, procedures need not be.
10. You can have DML(insert, update, delete) statements in 
a function. But, you cannot call 

such a function in a SQL query..eg: suppose, if u have a 
function that is updating a table.. 

you can't call that function in any sql query.
- select myFunction(field) from sometable;
will throw error.
11. Function parameters are always IN, no OUT is possible