On 2025-12-05 14:57 +0100, PG Doc comments form wrote: > The following documentation comment has been logged on the website: > > Page: https://www.postgresql.org/docs/17/ddl-generated-columns.html > Description: > > The documentation for generated columns in PostgreSQL versions prior to 18 > mention "virtual" columns, but as far as I can tell, this is not available > prior to 18. > > In v17, this is just in the first paragraph. > > > A generated column is a special column that is always computed from other > columns. Thus, it is for columns what a view is for tables. There are two > kinds of generated columns: stored and virtual. A stored generated column is > computed when it is written (inserted or updated) and occupies storage as if > it were a normal column. A virtual generated column occupies no storage and > is computed when it is read. Thus, a virtual generated column is similar to > a view and a stored generated column is similar to a materialized view > (except that it is always updated automatically). PostgreSQL currently > implements only stored generated columns.
The last sentence correctly states that Postgres v17- does not implement virtual columns. The paragraph is meant as a general overview because other RDBMS at that time had already implemented both flavors, e.g. SQLite. -- Erik Wienhold
