maria-developers team mailing list archive

[Sergei Golubchik <serg@xxxxxxxxxxx>]

Hi, Alexey!

On Nov 14, Alexey Botchkov wrote:
> Hi, Serg.
> 
> I'd like your opinion about this issue.
> Georg complains about weird column metadata
> https://jira.mariadb.org/browse/MDEV-10173
> 
> Personally i see slightly different result, but basically same thing.
> --------------------------------
> MariaDB [(none)]> select from_unixtime("0");
> Field   1:  `from_unixtime("0")`
> Catalog:    `def`
> Database:   ``
> Table:      ``
> Org_table:  ``
> Type:       DATETIME
> Collation:  binary (63)
> Length:     26
> Max_length: 19
> Decimals:   39
> Flags:      BINARY

Right, I get used to 31 being NOT_FIXED_DEC. But recently Monty changed
it to 39.

> +---------------------+
> | from_unixtime("0")  |
> +---------------------+
> | 1970-01-01 04:00:00 |
> +---------------------+
> 1 row in set (0.00 sec)
> --------------------------------
> 
> From what i see it is not a bug. The 'Decimals: 39' is not a real
> precision here, but just a hint to be flexible converting the data to
> the string.  The 'Length:  26' takes into account the possible
> 'second_part' of 6 digits.

Agree.

> Georg said on this: "Well, the client "trusts" the metadata. If there
> is decimal 31, it appends 31 decimal places and returned truncation
> error the metadata (MYSQL_FIELD) describes the data which are sent
> from server to client. If there are no decimal places, it should be
> zero. "

Yes, the cient trusts the metadata, but if decimals is NOT_FIXED_DEC it
means "unknown", not 31 (or 39).

If the number of decimals for a timestamp is unknown, the max length
is 26: "YYYY-MM-DD hh:mm:ss.uuuuuu"

> As an improvement i can see using '7' instead of '39' as an
> 'NOT_FIXED_DEC' marker for the Item_temporal_func.

Why? One wouldn't be able simply to compare with NOT_FIXED_DEC, it'll be
type dependent.

> Or we can just document that '39' value so clients interpret it right.

Isn't it documented?

> Serg, maybe you can suggest something?

Close as "Not a bug" :)

Regards,
Sergei
Chief Architect MariaDB
and security@xxxxxxxxxxx