From SAP Help:
Sales Group:
The definition of sales groups is optional. You can use the SD system without creating sales groups.
o You can assign a sales group to one or more sales offices.
Sales Office
The definition of sales offices is optional. You can use the SD System without creating sales offices.
o You assign a sales office to one or more sales areas.
Sales Organizaton
o Legally, a sales organization is included in exactly one company
code.
o You assign sales offices and your own employees to a sales
organization.
o All items in a sales & distribution document, that is, all items of
an order, delivery or a billing document belong to a sales
organization.
Summary
It looks like you have an hierachical structure starting at the Sales Org with a 0:N relationship to Sales Office which in turn have a 0:N relationship to Sales Group
Sales Group check table is TVKGR
Sales Office check table is TVBUR
Sales Org check table is TVKO