It is interesting that this should come up now. Just last week I was
trying to port a SQL statement from Oracle to Postgresql that used table
aliases in an update statement. While I can see that this functionality
wouldn't be used very often it can be very useful under certain
circumstances.
I have a table that stores a hierarchy. Sometimes in an update I want
to join back to the same table to get other information related to
children or parent rows. In Oracle I can do this using the alias, but
in Postgresql I cannot.
Consider the SQL statements below as simplistic examples of what I was
doing in Oracle:
table_foo foo_id int parent_foo_id int column_a int column_b int
update table_foo f1
set column_a = (select sum(column_a) from table_foo f2 where f2.parent_foo_id = f1.foo_id);
update table_foo f1
set column_b = 1
where exists (select column_a from table_foo f2 where f2.parent_foo_id = f1.foo_id);
thanks,
--Barry
Tom Lane wrote:
>
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Can someone comment on this?
> >>
> >> I just noticed that postgres doesn't totally support
> >> column aliases on UPDATE statements, for example
>
> The SQL92 spec very clearly does not allow an alias on the target table:
>
> 13.10 <update statement: searched>
>
> <update statement: searched> ::=
> UPDATE <table name>
> SET <set clause list>
> [ WHERE <search condition> ]
>
> While I'm willing to consider variations from the spec that add
> significant functionality, this proposed addition adds no functionality
> worth noticing. It'd just be another way to trip yourself up when
> moving across DBMSes.
>
> regards, tom lane