Arguments to insert][google.spanner.v1.Mutation.insert],
update][google.spanner.v1.Mutation.update],
[insert_or_update][google.spanner.v1.Mutation.insert_or_update], and
replace][google.spanner.v1.Mutation.replace] operations.
The names of the columns in
table][google.spanner.v1.Mutation.Write.table] to be written.
The list of columns must contain enough columns to allow Cloud
Spanner to derive values for all primary key columns in the
row(s) to be modified.