NEmacGuy is correct....the DRM is the best resource for field definitions.
In addition to oelinhst_sql, you may also wish to consider grabbing oehdrhst_sql and possibly your customer table (arcusfil_sql for Progression, cicmpy for ES) to get the most complete picture. When you join the history tables, make certain you join on ord_type, ord_no, and inv_no.
I actually create a view in my SQL database that joins everything together so I don't have to keep writing the same code over and over again.
Jen