Dear Sandeep Rajanala,
In general the existing ABAP code runs on SAP HANA as before. However if the existing ABAP Code relies on the technical specifics of the old database , ABAP Code changes might be necessary(which is the case for any database migration ).
For example,
- Your ABAP code uses a feature that is specific to the old database and not in the SQL standard and therefore not in Open SQL(consumed via Native SQL using EXEC SQL or ADBC interface)
- You have ABAP code that relies on unspecified undocumented implementation behaviour of the old database
the above cases may need minor code changes in ABAP during HANA migration.
The SAP note 1785057 gives guidelines on migrating the existing ABAP Custom Code for HANA.
Additionally we have several code inspector checks to find the ABAP code that requires changes and you can find details about these check in SAP note 1912445.
In addition you can find here an elaborate guide for transitioning custom ABAP code to HANA here.
You can also find the recording of the SAP Teched 2013 hands on which focuses completely on ABAP Custom Code migration aspect for HANA here
Hope this answers your question and gives you some pointers how you could prepare for the ABAP code transition for HANA.
Please revert back if you have further question.
Best Regards
Sundar.