Decide what to do with position-based param binding

[ChengyuanZhao]

Currently we do not support binding params by position since Spanner SQL does not support tags for position. We currently do not want to alter users' SQL.

[dzou]

From past discussions with Mark, it sounded like they did some mild parsing of named @ bind variables and then computed the index of the correct variable to use through parsing. This could be one approach we take.

[ChengyuanZhao]

I think we're all just concerned mild parsing can easily turn into mild-to-moderate or even moderate parsing

[elefeint]

Decided not to handle this for Spanner.