Thread

1. BUG #19019: Feature Request: allow the use of column reference in DEFAULT expression

   PG Bug reporting form <noreply@postgresql.org> — 2025-08-13T11:36:19Z

   The following bug has been logged on the website:
   
   Bug reference:      19019
   Logged by:          Paolo Saggese
   Email address:      spam@bit.bucket
   PostgreSQL version: Unsupported/Unknown
   Operating system:   Any
   Description:        
   
   As it is possible in some other SQL RDBMS, it would be useful to allow the
   use of column reference in DEFAULT expression.
   
   That is, for example:
   
   CREATE TABLE my_table
   (
       my_column my_type NOT NULL DEFAULT (  my_expression ),
       -- some other columns, constraints, etc...
   )
   
   where "my_expression" uses values from some other column(s) of (the same row
   of) the same table and may be allow (also) for even more generic references
   to any other column of any table in the DB (in which case "my_expression"
   would be a query returning a single value compatible with "my_type"...).
   
   A possible equivalent alternative syntax would be e.g.:
   
   GENERATED BY DEFAULT AS ( my_expression )
   
   (where "STORED" would be obviously implied...).
   
   Note that the (existing) syntax:
   
   GENERATED ALWAYS AS ( my_expression ) STORED
   
   obviously is not equivalent and does not provide the desired behavior (as of
   course in such case the column would be read-only and would not allow to
   replace the generated value with something else).
   
   

2. Re: BUG #19019: Feature Request: allow the use of column reference in DEFAULT expression

   David G. Johnston <david.g.johnston@gmail.com> — 2025-08-13T13:45:35Z

   On Wednesday, August 13, 2025, PG Bug reporting form <noreply@postgresql.org>
   wrote:
   
   > The following bug has been logged on the website:
   >
   > Bug reference:      19019
   > Logged by:          Paolo Saggese
   > Email address:      spam@bit.bucket
   > PostgreSQL version: Unsupported/Unknown
   > Operating system:   Any
   > Description:
   >
   > As it is possible in some other SQL RDBMS, it would be useful to allow the
   > use of column reference in DEFAULT expression.
   
   
   Our bug reporting system is not an appropriate channel to submit feature
   requests.  Send patches to -hackers or pleas to -general.
   
   David J.
   

3. Re: BUG #19019: Feature Request: allow the use of column reference in DEFAULT expression

   Laurenz Albe <laurenz.albe@cybertec.at> — 2025-08-14T04:53:28Z

   On Wed, 2025-08-13 at 11:36 +0000, PG Bug reporting form wrote:
   > As it is possible in some other SQL RDBMS, it would be useful to allow the
   > use of column reference in DEFAULT expression.
   
   You can use a BEFORE INSERT trigger for that.
   
   If you allow columns in a DEFAULT expression, would that use the column value
   from before or after the BEFORE triggers run?
   
   Yours,
   Laurenz Albe