If you want to show tableA.field and all tableB fields that "contain" tableA.field, you should use a subreport. This way, you could place tableA.field in details a section, and the subreport in details b.

The subreport must show tableB.field (and other fields you need). When inserting the subreport, use this settings in the Link tab: "Field(s) to link to": table1.field; "Subreport parameter field to use": choose the parameter proposed by Crystal, it begins with "?Pm-"; "Select data in subreport based on field" must be checked; finally choose tableB.field from the list a of tableB fields available. Click OK.

Now you have to modify the selection formula in the subreport. From the main report, Right click on the subreport --> Edit subreport. In the subreport, go to Select Expert and modify the selection formula, which must show something like
{Table2.Field} = {?Pm-Field}
Modify it to
{Table2.Field} like '*' + {?Pm-Field} + '*'
Now you should see all fields from table 2 that "contain" table1.field.

Maybe there are other solutions, but this one seems simple.