Hi Joe,
Thanks for the quick response and for taking the time to investigate my question.
Your correct, the SUPPCREDIT transactions ARE being picked up in your query, and also in my tax query. Sorry for wasting your time.
I had been comparing the Tax Inquiry report against a GL Inquiry of my VAT account, and saw differences. In the Tax Query, the Credit Note VAT amounts show in the Collectable column, whereas in the GL Inquiry, they show in the Credit column. So I was getting different summation figures. I had a quick look at the gl_db_trans.inc file, and as I did'nt see the SUPPCREDIT constant, I assumed that was the problem. Looking in detail at your supplied query, I see that these constants are only used to get the sign correct for the calculations, not to restrict the search.
Thanks again for your help.