Give me some examples of user exit that is applied in MM area in a real time scenario.

1. User exits can be found out using a development class or a package. 
2. For which transaction you would like know whether user exit is available or not.
example 1. Whenever I create a purchase order my vendor is same for a particular purchasing group and a particular purchasing organization .

Procedure to find out the user exit :
3.For which transaction you would like to see the user exits, frrst goto transaction and click system status and find out the technical name i.e is package.
4. By going to the SMOD transaction give package name and find out the real user exits available or not.  Once it is available go to edit attributes and write program by givng the filed name = '9999' (some vendor) and save , click, save, activte.
5. Go top CMOD  transaction and give that user exit in the filed area and activate .
6. Go and observe in me21 and see that 9999 vendor by default will come when ever you will create po.

*-- Pinnapati Hari Prasad 

To Develop Enhancements for Purchasing  In this step, you develop enhancements for Purchasing.

1. Either create a new project or use an existing one and then enter the enhancement.
2. Activate the project - Your enhancement will only become effective after activation.

In contrast to modifications, enhancements are basically release-insensitive since they are not implemented in the SAP original but in a name range that is reserved for the customer.  If you want to display the documentation for an enhancement, choose Goto -> Documentation in the enhancement transaction.

The following SAP enhancements are available for the Purchasing area:

AMPL0001 - User subscreen for additional AMPL data (manufacturer part number)

LMELA002 - Adoption of batch number from shipping notification at time of posting of a goods receipt

LMELA010 - Incoming shipping notification: adoption of item data from IDoc

LMEQR001 - User exit for source determination

M06B0001 - Role determination for release of requisitions

M06B0001 - Changes to communication structure for release of requisitions

M06B0003 - Number range and document number

M06B0004 - Number range and document number

M06B0005 - Changes to communication structure for overall release of purchase requisitions

M06E0004 - Changes to communication structure for release of purchasing document

M06E0005 - Role determination for release of purchasing documents

ME590001 - Grouping of requisitions for PO split in transaction ME59

MEETA001 - Determination of schedule line type (backlog, immediate requirement, forecast)

MEFLD004 - Determination of earliest delivery date for checking at time of goods receipt (PO only)

MELAB001 - Generation of forecast delivery schedule: realization via creation profile

MEQUERY1 - Enhancement for document overview ME21N / ME51N

MEVME001 - Calculation of default GR quantity and over/underdelivery tolerances

MM06E001 - User exits for inbound EDI messages and outbound purchasing documents

MM06E003 - Number range and document number

MM06E004 - Control of import data screens in purchase orders

MM06E005 - Customer fields in purchasing documents

MEREQ001 - Customer's own data in purchase requisitions

MM06E007 - Change document for requisitions when converting into POs

MM06E008 - Monitoring of contract target value in case of release orders

MM06E009 - Relevant texts for "Texts exist" indicator

MM06E010 - Field selection for vendor address

MM06E011 - Activation of requisition block

MM06L001 - Exits for determination of ratings in vendor evaluation

MMAL0001 - ALE source list distribution: outbound processing

MMAL0002 - ALE source list distribution: inbound processing

MMAL0003 - ALE purchasing info record distribution: outbound processing

MMAL0004 - ALE purchasing info record distribution: inbound processing

MMDA0001 - Default values for delivery addresses

MMFAB001 - User exit for generation of releases

MRFLB001 - Control items during release creation

LWBON001 - Enhancement of LIS update through extension of the communication structure MCKONA (business volumes and rebate income)

LWBON003 - Change settlement data for end-of-period rebate settlement before creation of settlement documents

LWSUS001 - Customer-specific source determination in Retail

LMEXF001 - Conditions in purchasing documents without invoice receipt

LMEKO002 - Enhance communication structure KOMP for price determination                 *-- Pandey Ajai

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