(disclosure: CockroachDB founder) The reason I've heard is that Spanner uses a separate mutation API instead of SQL DML because of a quirk of its transaction model. Writes within a transaction are not visible to subsequent reads within the same transaction (source: https://cloud.google.com/spanner/docs/transactions#rw_transa...). This is different from other SQL databases, so the use of a different API forces you to think about your read/write transactions in a Spanner-specific way.

(FWIW, CockroachDB does not have this limitation - transactions can read their own uncommitted writes, just like in other databases)

+1, also curious about this. I speculated that Cloud Spanner is supposed to be F1[1], but the fact that F1 seems to fully support SQL DML makes this difference even more perplexing.

> Updates are also supported using SQL data manipulation statements, with extensions to support updating fields inside protocol buffers and to deal with repeated structure inside protocol buffers.

[1] https://research.google.com/pubs/pub41344.html