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Posted to dev@hive.apache.org by Shyam Sarkar <sh...@yahoo.com> on 2009/02/11 23:37:12 UTC
Need LOCALTIMESTAMP ?
Hello,
Please help me to understand what I am going to implement for Timestamp. Do we need LOCALTIMESTAMP implementation? See the comparisons below::
=================================================================
LOCALTIMESTAMP
It's often important to get the value of current date and time. Below are the functions used to do that in the different implementations.
Standard The current timestamp (without time zone) is retrieved with the LOCALTIMESTAMP function which may be used as:
SELECT LOCALTIMESTAMP ...
or
SELECT LOCALTIMESTAMP(precision) ...
Note that "SELECT LOCALTIMESTAMP() ..." is illegal: If you don't care about the precision, then you must not use any parenthesis.
If the DBMS supports the non-core time zone features (feature ID F411), then it must also provide the functions CURRENT_TIMESTAMP and CURRENT_TIMESTAMP(precision) which return a value of type TIMESTAMP WITH TIME ZONE. If it doesn't support time zones, then the DBMS must not provide a CURRENT_TIMESTAMP function.
PostgreSQL Follows the standard.
Documentation
DB2 Doesn't have the LOCALTIMESTAMP function.
Instead, it provides a special, magic value ('special register' in IBM language), CURRENT_TIMESTAMP (alias to 'CURRENT TIMESTAMP') which may be used as though it were a function without arguments. However, since DB2 doesn't provide TIMESTAMP WITH TIME ZONE support, the availability of CURRENT_TIMESTAMP could be said to be against the standard—at least confusing.
Documentation
MSSQL Doesn't have the LOCALTIMESTAMP function.
Instead, it has CURRENT_TIMESTAMP which—however—doesn't return a value of TIMESTAMP WITH TIME ZONE, but rather a value of MSSQL's DATETIME type (which doesn't contain time zone information).
Documentation
MySQL Follows the standard.
Documentation
Oracle Follows the standard.
Informix On my TODO.
====================================================================
Thanks,
shyam_sarkar@yahoo.com
RE: Need LOCALTIMESTAMP ?
Posted by Shyam Sarkar <sh...@yahoo.com>.
Hi Ashish,
Read about the latest TIMESTAMP implementation in MySQL 5.0 version and suggest ::
http://dev.mysql.com/doc/refman/5.0/en/timestamp.html
Also please comment on the following MySQL 5.0 implementation semantics::
"TIMESTAMP values are converted from the current time zone to UTC for storage, and converted back from UTC to the current time zone for retrieval. (This occurs only for the TIMESTAMP data type, not for other types such as DATETIME.) By default, the current time zone for each connection is the server's time."
Should we do the same thing?
Thanks,
shyam_sarkar@yahoo.com
--- On Wed, 2/11/09, Ashish Thusoo <at...@facebook.com> wrote:
> From: Ashish Thusoo <at...@facebook.com>
> Subject: RE: Need LOCALTIMESTAMP ?
> To: "hive-dev@hadoop.apache.org" <hi...@hadoop.apache.org>, "shyam_sarkar@yahoo.com" <sh...@yahoo.com>
> Date: Wednesday, February 11, 2009, 2:55 PM
> Hi Shyam,
>
> I think HIVE-192 is about the fact that there is no support
> for the timestamp type in Hive (or for that matter date and
> datetime types). In FB we are using strings to hold this
> information.
>
> If you are planning to add a built in function like
> localtimestamp, then that should probably go into a
> different JIRA.
>
> We have tried to adhere to mysql way of doing things as we
> find more folks using it (at least in our company) and looks
> from your research that they are basically standards
> compliant. So my vote will be to go with mysql semantics and
> CURRENT_TIMESTAMP construct.
>
> Ashish
>
>
> -----Original Message-----
> From: Shyam Sarkar [mailto:shyam_sarkar@yahoo.com]
> Sent: Wednesday, February 11, 2009 2:37 PM
> To: hive-dev@hadoop.apache.org
> Subject: Need LOCALTIMESTAMP ?
>
> Hello,
>
> Please help me to understand what I am going to implement
> for Timestamp. Do we need LOCALTIMESTAMP implementation? See
> the comparisons below::
>
> =================================================================
>
>
> LOCALTIMESTAMP
> It's often important to get the value of current date
> and time. Below are the functions used to do that in the
> different implementations.
>
> Standard The current timestamp (without time zone) is
> retrieved with the LOCALTIMESTAMP function which may be used
> as:
> SELECT LOCALTIMESTAMP ...
> or
> SELECT LOCALTIMESTAMP(precision) ...
>
> Note that "SELECT LOCALTIMESTAMP() ..." is
> illegal: If you don't care about the precision, then you
> must not use any parenthesis.
>
> If the DBMS supports the non-core time zone features
> (feature ID F411), then it must also provide the functions
> CURRENT_TIMESTAMP and CURRENT_TIMESTAMP(precision) which
> return a value of type TIMESTAMP WITH TIME ZONE. If it
> doesn't support time zones, then the DBMS must not
> provide a CURRENT_TIMESTAMP function.
>
> PostgreSQL Follows the standard.
> Documentation
>
> DB2 Doesn't have the LOCALTIMESTAMP function.
> Instead, it provides a special, magic value ('special
> register' in IBM language), CURRENT_TIMESTAMP (alias to
> 'CURRENT TIMESTAMP') which may be used as though it
> were a function without arguments. However, since DB2
> doesn't provide TIMESTAMP WITH TIME ZONE support, the
> availability of CURRENT_TIMESTAMP could be said to be
> against the standard-at least confusing.
>
> Documentation
>
> MSSQL Doesn't have the LOCALTIMESTAMP function.
> Instead, it has CURRENT_TIMESTAMP which-however-doesn't
> return a value of TIMESTAMP WITH TIME ZONE, but rather a
> value of MSSQL's DATETIME type (which doesn't
> contain time zone information).
>
> Documentation
>
> MySQL Follows the standard.
> Documentation
>
> Oracle Follows the standard.
> Informix On my TODO.
>
> ====================================================================
>
> Thanks,
> shyam_sarkar@yahoo.com
RE: Need LOCALTIMESTAMP ?
Posted by Ashish Thusoo <at...@facebook.com>.
Hi Shyam,
I think HIVE-192 is about the fact that there is no support for the timestamp type in Hive (or for that matter date and datetime types). In FB we are using strings to hold this information.
If you are planning to add a built in function like localtimestamp, then that should probably go into a different JIRA.
We have tried to adhere to mysql way of doing things as we find more folks using it (at least in our company) and looks from your research that they are basically standards compliant. So my vote will be to go with mysql semantics and CURRENT_TIMESTAMP construct.
Ashish
-----Original Message-----
From: Shyam Sarkar [mailto:shyam_sarkar@yahoo.com]
Sent: Wednesday, February 11, 2009 2:37 PM
To: hive-dev@hadoop.apache.org
Subject: Need LOCALTIMESTAMP ?
Hello,
Please help me to understand what I am going to implement for Timestamp. Do we need LOCALTIMESTAMP implementation? See the comparisons below::
=================================================================
LOCALTIMESTAMP
It's often important to get the value of current date and time. Below are the functions used to do that in the different implementations.
Standard The current timestamp (without time zone) is retrieved with the LOCALTIMESTAMP function which may be used as:
SELECT LOCALTIMESTAMP ...
or
SELECT LOCALTIMESTAMP(precision) ...
Note that "SELECT LOCALTIMESTAMP() ..." is illegal: If you don't care about the precision, then you must not use any parenthesis.
If the DBMS supports the non-core time zone features (feature ID F411), then it must also provide the functions CURRENT_TIMESTAMP and CURRENT_TIMESTAMP(precision) which return a value of type TIMESTAMP WITH TIME ZONE. If it doesn't support time zones, then the DBMS must not provide a CURRENT_TIMESTAMP function.
PostgreSQL Follows the standard.
Documentation
DB2 Doesn't have the LOCALTIMESTAMP function.
Instead, it provides a special, magic value ('special register' in IBM language), CURRENT_TIMESTAMP (alias to 'CURRENT TIMESTAMP') which may be used as though it were a function without arguments. However, since DB2 doesn't provide TIMESTAMP WITH TIME ZONE support, the availability of CURRENT_TIMESTAMP could be said to be against the standard-at least confusing.
Documentation
MSSQL Doesn't have the LOCALTIMESTAMP function.
Instead, it has CURRENT_TIMESTAMP which-however-doesn't return a value of TIMESTAMP WITH TIME ZONE, but rather a value of MSSQL's DATETIME type (which doesn't contain time zone information).
Documentation
MySQL Follows the standard.
Documentation
Oracle Follows the standard.
Informix On my TODO.
====================================================================
Thanks,
shyam_sarkar@yahoo.com