Dear PatentsView Community:

I would like to filter the approximately 7.7M granted patents in g_patent to specific CPC codes. After filtering g_patent to utility patents, which are the patents of interest to me, I think I need to join CPC codes from g_cpc_at_issue, which contains approximately 20.0M rows, to patents from g_patent to filter by CPC code. I have three questions to help:

1. Can you provide a brief description of g_cpc_at_issue? The table description column on PatentsView's Data Download Tables page is blank for g_cpc_at_issue. Generally, would CPC codes in g_cpc_at_issue be appropriate for filtering?
2. The name g_cpc_at_issue suggests that the CPC codes in this table are the codes given to a patent at the time it was issued and might not be the codes that would be given to a patent under the current CPC system. The name of another table on the Data Download Tables page, g_cpc_current, suggests that this table might have codes given to a patent under the current CPC system, although it contains a relatively small number of rows (<250K) relative to g_patent. Can you suggest how (if at all) g_cpc_current should be used in combination with g_cpc_at_issue to attach current CPC codes to granted patents from g_patent?
3. g_cpc_at_issue contains a variable called cpc_type, which is populated with 'additional' and 'inventional'. This post says that 'inventional' means a CPC code is directly related to an invention and 'additional' means a CPC code is not directly related to an invention. g_cpc_at_issue also contains a variable called cpc_sequence. This post indicates that cpc_sequence == 1 means that a CPC code is the primary classification for a patent. Thus, if I would like to filter patents by the CPC code that best represents the subject matter of the patent, then I think I would need to use CPC codes where cpc_type == 'inventional' and cpc_sequence == 1. Can you say whether this is correct?

Thanks in advance for your help, and for making PatentsView an amazing resource!