Re: No JOINs in UPDATE ... FROM?

Josh Berkus <josh(at)agliodbs(dot)com> writes:
> UPDATE assignments SET status = -1
> FROM assignments JOIN orders ON assignments.order_usq = orders.usq
> WHERE orders.status = -1;

> However, I get an error of "Relation assignments referenced twice in
> query."

> Now, I can (and have) re-phrase the query so that PostgreSQL will
> accept it. However, I was under the impression that the above was
> standard SQL92. Am I mistaken?

You are mistaken. SQL92 and SQL99 don't allow a FROM clause in UPDATE
at all: they say it's just

<update statement: searched> ::=
UPDATE <target table>
SET <set clause list>
[ WHERE <search condition> ]

Postgres allows the clause, but treats it as supplying *additional*
table references besides the target table reference. Thus the error.

In other words: you can JOIN, but not against the target table.

regards, tom lane