Re: Question about copy from with timestamp format - Mailing list pgsql-general

On 07/30/2015 08:44 AM, Sherrylyn Branchaw wrote:

I was thinking that perhaps an updatable view might do the trick?

Interesting idea! Are you able to get it to work? I keep getting 'ERROR:
  cannot copy to view "view_ts_test"' even before my trigger fires.
Inserting, though, works fine.

From here:

http://www.postgresql.org/docs/9.4/interactive/sql-copy.html

"COPY can only be used with plain tables, not with views. However, you can write COPY (SELECT * FROM viewname) TO ...."

Still curious why the triggers I'm writing won't fire before my
statement errors out on copying to a view, or inserting an out-of-range
timestamp, when the trigger would resolve all the illegal operations if
it just fired first.

On Thu, Jul 30, 2015 at 5:57 AM, Alban Hertroys <haramrae@gmail.com
<mailto:haramrae@gmail.com>> wrote:


    > On 30 Jul 2015, at 2:27, Sherrylyn Branchaw <sbranchaw@gmail.com <mailto:sbranchaw@gmail.com>> wrote:
    >
    > Based on your PS asking about data types and commenting that you don't want to put hour in a separate column, it sounds like this is a brand-new table you're creating. If so, and if this is a one-time COPY operation, you can create a text column for the initial import. Then after you're done importing, you can execute
    >
    > ALTER TABLE ts_test ALTER COLUMN ts_fld TYPE TIMESTAMP USING (to_timestamp(ts_fld, 'YYYYMMDDHH24'));
    >
    > to convert the format of the imported data to a timestamp. Then you're set.
    >
    > If there will be ongoing imports of more files like this, though, you'll need the intermediate table solution offered by Adrian.

    Or keep both columns and update those where the text-column is NOT
    NULL and the timestamp column is NULL.

    > I was going to suggest a trigger, but it turns out that the data type checking happens even before the BEFORE trigger fires, so you don't get a chance to massage your data before actually inserting it. I got 'ERROR:  date/time field value out of range: "2015072913 <tel:2015072913>"' before the trigger even fired. I
    wonder if that's deliberate? I was able to implement a workaround by
    adding a raw_ts_fld column of type text, but an extra column might
    be too ugly for you relative to a temp table, I don't know.

    I was thinking that perhaps an updatable view might do the trick?

    You would need to create a view with the timestamp column converted
    to text in the format in your CSV file. Next you add an INSERT rule
    that does the conversion from text to timestamp and inserts the row
    in the actual table. Finally, you use the view in the COPY statement
    instead of the table.
    Added bonus, you can now also use the view to export your table to
    the same CSV format.

    Alban Hertroys
    --
    If you can't see the forest for the trees,
    cut the trees and you'll find there is no forest.

--
Adrian Klaver
adrian.klaver@aklaver.com