Обсуждение: Trying to convert a TIMESTAMP return value to TIME

I have a table with a column of type TIME, and I am trying to insert a
row into it in the following manner:

INSERT INTO EVENTS (EVENT_ID, EVENT_TIME, TITLE) VALUES ('20394XCB',
TO_TIMESTAMP('10:45', 'HH:MI'), 'An Event');

I get the following error: 'column "event_time" is of type 'time
without time zone' but expression is of type 'timestamp with time
zone' You will need to rewrite or cast the expression'.

I have looked extensively at the PostgreSQL documentation, and have
failed to find any info on how to get a TIME value out of a TIMESTAMP,
or else how to convert a CHAR time like '10:45' directly to a TIME. 
The suggestion about casting given by the error message was
tantalizing, but I don't know how to make the cast happen.

Any clues or ideas from Pgsql gurus?  TKA.

-Erik Norvelle

--------------------------------------------
Erik Norvelle
Support Systems Analyst, Sr.
Distributed Learning Laboratory
Educational Communications and Technologies
College of Agriculture and Life Sciences
The University of Arizona
--------------------------------------------
Credo in Unum Deum
--------------------------------------------

norvelle@ag.arizona.edu (Erik Norvelle) writes:
> I get the following error: 'column "event_time" is of type 'time
> without time zone' but expression is of type 'timestamp with time
> zone' You will need to rewrite or cast the expression'.

> I have looked extensively at the PostgreSQL documentation, and have
> failed to find any info on how to get a TIME value out of a TIMESTAMP,
> or else how to convert a CHAR time like '10:45' directly to a TIME. 

A little bit of experimentation found that you can get there indirectly
by casting first to time-with-time-zone:

regression=# select TO_TIMESTAMP('10:45', 'HH:MI');   to_timestamp
---------------------0001-01-01 10:45 BC
(1 row)

regression=# select TO_TIMESTAMP('10:45', 'HH:MI')::time;
ERROR:  Cannot cast type 'timestamp with time zone' to 'time without time zone'
regression=# select TO_TIMESTAMP('10:45', 'HH:MI')::timetz;to_timestamp
--------------10:45:00+00
(1 row)

regression=# select TO_TIMESTAMP('10:45', 'HH:MI')::timetz::time;to_timestamp
--------------10:45:00
(1 row)

However, if you don't need the formatting control of to_timestamp
(ie, the input data should be valid time input anyway), why not
forget to_timestamp and just cast text to time?

regression=# select '10:45'::text::time;  time
----------10:45:00
(1 row)
        regards, tom lane

I'm posting a followup to my own message to indicate the solution I
found.  I found I had to use the CAST operator, as follows:

INSERT INTO EVENTS (EVENT_ID, EVENT_TIME, TITLE) VALUES ('20394XCB',
CAST(TO_TIMESTAMP('10:45', 'HH:MI') AS TIME WITH TIME ZONE), 'An
Event');

Apparently, once the timestamp has been cast to TIME WITH TIME ZONE,
PostgreSQL can figure out how to convert to a standard TIME type (ie.
no timezone).

-Erik Norvelle

norvelle@ag.arizona.edu (Erik Norvelle) wrote in message news:<48367cfb.0202201935.3dc51c8a@posting.google.com>...
> I have a table with a column of type TIME, and I am trying to insert a
> row into it in the following manner:
> 
> INSERT INTO EVENTS (EVENT_ID, EVENT_TIME, TITLE) VALUES ('20394XCB',
> TO_TIMESTAMP('10:45', 'HH:MI'), 'An Event');
> 
> I get the following error: 'column "event_time" is of type 'time
> without time zone' but expression is of type 'timestamp with time
> zone' You will need to rewrite or cast the expression'.
> 
> I have looked extensively at the PostgreSQL documentation, and have
> failed to find any info on how to get a TIME value out of a TIMESTAMP,
> or else how to convert a CHAR time like '10:45' directly to a TIME. 
> The suggestion about casting given by the error message was
> tantalizing, but I don't know how to make the cast happen.
> 
> Any clues or ideas from Pgsql gurus?  TKA.
> 
> -Erik Norvelle
> 
> --------------------------------------------
> Erik Norvelle
> Support Systems Analyst, Sr.
> Distributed Learning Laboratory
> Educational Communications and Technologies
> College of Agriculture and Life Sciences
> The University of Arizona
> --------------------------------------------
> Credo in Unum Deum
> --------------------------------------------