SQL99 part 2 clause 16.1 contains this note:
NOTE 327 - The characteristics of a transaction begun by a <start transaction statement> are as specified in these
General Rules regardless of the characteristics specified by any preceding <set transaction statement>. That is,
evenif one or more characteristics are omitted by the <start transaction statement>, the defaults specified in the
SyntaxRules of this Subclause are effective and are not affected by any (preceding) <set transaction statement>.
In other words, this should work:
peter=# set session characteristics as transaction read only;
SET
peter=# start transaction;
START TRANSACTION
peter=# create table test (a int);
ERROR: transaction is read-only
because the default of a bare "start transaction" is read write. I
propose that we change this to follow the standard and keep the
traditional behavior for BEGIN only.