> > From: Tom Lane <t...@sss.pgh.pa.us> > David G Johnston <david.g.johns...@gmail.com> writes: >> Two approaches: >> 1. Standard virtual column name that, when used, gets rewritten into a >> constant that is stored at the table level. >> 2. A way for a column's value to be defined as a function call. > > Recent versions of the SQL spec have a notion of "generated columns" > that I think subsumes both of these concepts. We had a draft patch > awhile back that attempted to implement that feature. It crashed > and burned for reasons I don't recall ... but certainly implementing > an already-standardized feature is more attractive than just inventing > behavior on our own. >
That sounds interesting. Is this what you are referring to? Actually, it looks like it would fit the bill and then some. ————————————————— 4.14.8 Base columns and generated columns A column of a base table is either a base column or a generated column. A base column is one that is not a generated column. A generated column is one whose values are determined by evaluation of a generation expression, a <value expression> whose declared type is by implication that of the column. A generation expression can reference base columns of the base table to which it belongs but cannot otherwise access SQL- data. Thus, the value of the field corresponding to a generated column in row R is determined by the values of zero or more other fields of R. A generated column GC depends on each column that is referenced by a <column reference> in its generation expression, and each such referenced column is a parametric column of GC. —————————————————
