Not super sure if it follows any of them, but it might be ANSI 2011, since Cloud Spanner SQL is described as "ANSI 2011 with extensions", and I would expect that to be a strict subset of ZetaSQL.
For some more context, ZetaSQL is the thing we've standardized our internal systems on, aka F1, Dremel/BigQuery, Spanner (and there's a few others). The F1 Query paper makes a light reference to this in S7.2 http://www.vldb.org/pvldb/vol11/p1835-samwel.pdf.
EDIT: BigQuery SQL is described as "compliant with the SQL 2011 standard and has extensions", and I would also expect that to be a strict subset of ZetaSQL.
For some more context, ZetaSQL is the thing we've standardized our internal systems on, aka F1, Dremel/BigQuery, Spanner (and there's a few others). The F1 Query paper makes a light reference to this in S7.2 http://www.vldb.org/pvldb/vol11/p1835-samwel.pdf.
For me, the most valuable feature of it has been that protos are an explicitly defined data type, since we use protos for pretty much everything. Docs: https://github.com/google/zetasql/blob/master/docs/one-pager...
EDIT: BigQuery SQL is described as "compliant with the SQL 2011 standard and has extensions", and I would also expect that to be a strict subset of ZetaSQL.