Re: To create a Column ina Table with function

csanyipal@gmail.com wrote:
> I have a table with columns: number, date-range.
> I wish to get in this table more columns: week-day-begin, week-day-end.
> 
> In the week-day-begin column I wish to get automatically the weekday
> name of the first date in the date range.
> 
> In the week-day-end column I wish to get automatically the weekday
> name of the last date in the date range.
> 
> How can I get these two columns by executing a function?
> Should this function be a Dynamic Command, or a trigger?

If you really need those columns materialized, it would be a trigger
BEFORE INSERT OR UPDATE FOR EACH ROW.

But why not use a view? It is normally a bad idea to keep
redundant information around.

CREATE TABLE test (i integer PRIMARY KEY, dr daterange NOT NULL);

CREATE VIEW testview AS
   SELECT i, dr,
          EXTRACT(DOW FROM lower(dr)) AS wd_start,
          EXTRACT(DOW FROM upper(dr)) AS wd_end
   FROM test;

INSERT INTO test VALUES (1, '[1968-10-20,2050-04-01]');

SELECT * FROM testview;

 i |           dr            | wd_start | wd_end
---+-------------------------+----------+--------
 1 | [1968-10-20,2050-04-02) |        0 |      6
(1 row)

Yours,
Laurenz Albe