Support Partitioned DML

[yfuruyama]

Cloud Spanner has two execution modes for DML, DML and Partitioned DML, but currently spanner-cli only supports normal DML. It would be better to support Partitioned DML in spanner-cli since it can process large-scale operations over the entire rows.

One thing we might need to discuss would be syntax for executing a Partitioned DML.

Context: #92 (comment)

[yfuruyama]

@apstndb You mentioned EXECUTE PARTITIONED (INSERT|UPDATE|DELETE) ... as an example for the syntax in #92 (comment), but what is the rationale behind it?

I'm wondering if we can make it simpler by just saying PARTITIONED (INSERT|UPDATE|DELETE) ... to indicate executing the DML as a Partitioned DML.

[apstndb]

EXECUTE PARTITIONED (INSERT|UPDATE|DELETE) is inspired by EXECUTE IMMEDIATE but only for example and no rationale.
It may be even wrong because of ambiguous syntax with the standard Dynamic SQL(EXECUTE IMMEDIATE, PREPARE and EXECUTE).

I want to vote PARTITIONED (INSERT|UPDATE|DELETE) ... because it is simple and unambiguous.

[yfuruyama]

Sounds good, then let's use PARTITIONED (INSERT|UPDATE|DELETE) ... for the syntax. I'll take on this.