Differences between user defined functions and stored procedures are:

* Stored procedures does not return any data and they can not be used in expressions.

* User defined functions does return data and they can be used in expressions.

* Stored procedures only takes data constants as input parameters.

* User defined functions can take data constants and expressions as input parameters.

* Stored procedures support output parameters.

* User defined functions do not support output parameters.

* Stored procedures take a parameter's default value, if it is not specified in the calling statement.

* User defined functions take a parameter's default value, if it is specified with the keyword DEFAULT in the calling statement.

* Stored procedures are called with no parenthesis to include parameters.

* User defined functions are called with parenthesis to include parameters. Empty parenthesis is needed if no parameters.

* Stored procedures can be created locally and temporarily.

* User defined functions can not be created locally and temporarily.