Crystal Reports inventory audit report show base and target doc

Message

     I am rookie of SAP and crystal report. My boss want the inventory audit report can show the base document and target document. 

At
 Begin, I started to using crystl report to buildup the origin view of 
inventory audit report but i find the problem in links to the base 
document. I using able is OINM, Base_REF and i want to link this 
document of base document.

Example: inventory audit repory shows 
the document is DN-xxxxxxx , i want find the base and target document of
 this DN-xxxxxx. But it contain other many document. Also when i try 
links OINM, Base_REF to ODLN,DocNum, it can't. I think the reasons is 
OINM, Base_REF is char and ODLN,DocNum is str. How can slove it? Sorry 
of ask to many question. 