1.e4 was the most common opening, representing 70% of the sample. This was followed by 1.d4, representing 20%. This frequency goes up as more master games are included and amateur games excluded.
The next most common was 1.c4, representing 5% of the sample. Again, this number goes up with more master games and less amateur games. But our sample represents chess at all levels.
The next most common was 1.Nf3, representing 4% of the sample. Thus, 1.e4, 1.d4, 1.c4, and 1.Nf3 represent 99% of all openings in most databases.
The next most common was 1.b3, closely followed by 1.b4, 1.f4 and 1.g3. These openings represented .9% of the sample.
Next came 1.Nc3, 1.g4, 1.e3, 1.Na3, and 1.Nh3
The rarest moves were 1.a3, 1.c3, 1.f3, 1.h4, 1.d3, 1.a4, and finally 1.h3.
The most common response to 1.e4 was 1...e5. The next most common was 1...c5.
Next came 1...e6, followed by 1...c6.
Next in frequency was 1...Nf6, 1...d5, then 1...d6.
Next came 1...g6, 1...Nc6, followed by 1...b6.
Then came 1...a6, then 1...g5.
Finally, the rarest moves were 1...f6, 1...a5, 1...Nh6, 1...Na6, 1...f5, 1...h5, and 1...h6. I found no 1...b5 move.
The most common response to 1.d4 was 1...Nf6, followed closely with 1...d5.
Next came 1...f5. These 3 moves represent over 90% of the responses to 1.d4.
Next in frequency was 1...e6, followed by 1...c5.
Still rarer were 1...b6, 1...b5, 1...d6, 1...Nc6, 1...g6, and 1...e5
Finally, the rarest moves were 1...c6, 1...h6, 1...Nh6, and 1...f6.
I found no 1...a5, 1...a6, 1...Na6, 1...g5, or 1...h5.