How to do purchasing inter company and without inter company with the same vendor?
Normally when we create PO with inter company we are getting automatically Goods issuee also.
However some time we need to create normal purchase order without goods issue.  Is there any customization is required?

To the best of my knowledge, is that it is impossible. Once the a vendor is assigned to a plant, the PO is assumed to be a STO.

The only way to buy sometimes as STO and sometimes as from external vendor is to have two different vendor numbers for the same vendor. You can group their invoices (MIRO) automatically to the same vendor account using the "Head office" field in the vendor master.

Please go through the following path:

XK02 -> Enter Vendor code, company code and purchase organization -> Select the Accounting Info Check box -> Press Enter -> In the screen you can find the Head office field below the Recon. account field. 

OR 

Go to " OMSX " 

Here select "Vendor accounting" and click on Details button.

Now click on "Account management " selection group.

Here you can make the indicator for Head office filed as Mandatory/Optional if it is in Suppress mode.

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