Class TypeCode (3.50.0)

    If the schema has the column option
    `allow_commit_timestamp=true`, the placeholder string
    `"spanner.commit_timestamp()"` can be used to instruct the
    system to insert the commit timestamp associated with the
    transaction commit.
DATE (5):
    Encoded as `string` in RFC 3339 date format.
STRING (6):
    Encoded as `string`.
BYTES (7):
    Encoded as a base64-encoded `string`, as described in RFC
    4648, section 4.
ARRAY (8):
    Encoded as `list`, where the list elements are represented
    according to
    `array_element_type][google.spanner.v1.Type.array_element_type]`.
STRUCT (9):
    Encoded as `list`, where list element `i` is represented
    according to
    [struct_type.fields[i]][google.spanner.v1.StructType.fields].
NUMERIC (10):
    Encoded as `string`, in decimal format or scientific
    notation format. Decimal format: `[+-]Digits[.[Digits]]`
    or `[+-][Digits].Digits`

    Scientific notation:
    `[+-]Digits[.[Digits]][ExponentIndicator[+-]Digits]` or
    `[+-][Digits].Digits[ExponentIndicator[+-]Digits]`
    (ExponentIndicator is `"e"` or `"E"`)
JSON (11):
    Encoded as a JSON-formatted `string` as described in RFC
    7159. The following rules are applied when parsing JSON
    input:

    -  Whitespace characters are not preserved.
    -  If a JSON object has duplicate keys, only the first key
       is preserved.
    -  Members of a JSON object are not guaranteed to have their
       order preserved.
    -  JSON array elements will have their order preserved.
PROTO (13):
    Encoded as a base64-encoded `string`, as described in RFC
    4648, section 4.
ENUM (14):
    Encoded as `string`, in decimal format.
INTERVAL (16):
    Encoded as `string`, in `ISO8601` duration format -
    `P[n]Y[n]M[n]DT[n]H[n]M[n[.fraction]]S` where `n` is an
    integer. For example, `P1Y2M3DT4H5M6.5S` represents time
    duration of 1 year, 2 months, 3 days, 4 hours, 5 minutes,
    and 6.5 seconds.