Re: Subqueries in Non-SELECT Queries

Frank Joerdens <frank@joerdens.de> writes:
> mpi=# update index set level = 2 where parentid = ( select id from
> index where level = 1 );
> ERROR:  More than one tuple returned by a subselect used as an expression.

Apparently the subquery "select id from index where level = 1" is
returning more than one row.  Perhaps you want WHERE parentid IN subselect
rather than WHERE parentid = subselect.  "=" is a scalar operator, not
a set operator.
        regards, tom lane