BSEG is not a great table to search for data on due to it's definition as a cluster table. i.e. There is no physical table in the database called BSEG (in fact most data is stored in a table called RFBLG).

If you can use the document header table, BKPF then ... 

Rather use the following: 

• BSID Accounting: Secondary Index for Customers(Open Items)
• BSIK Accounting: Secondary Index for Vendors
• BSIM Secondary Index, Documents for Material
• BSIS Accounting: Secondary Index for G/L Accounts
• BSAD Accounting: Secondary Index for Customers(Cleared Items)
• BSAK Accounting: Secondary Index for Vendors(Cleared Items)
• BSAS Accounting: Secondary Index for G/L Accounts(Cleared Items)