This observation may or may not be helpful.

I couldn't help but notice your WHERE clause:

"WHERE

a.P_STATUS <> 'R'

and b.TICKET_NUM is not null

and b.TXN_DT is not null"

All NOT comparisons cause scans instead of seeks. If you can find some way to avoid performing NOT comparisons, it would likely improve the performance of your query, if you have properly implemented supporting indexes. To what degree will depend on the sizes of your tables.