Tracker reference CORE-2580

Previously, a subquery used as a PSQL expression would return an exception, even though it was logically valid in SQL terms. For example, the following constructions would all return errors:

var = (select ... from ...);
if ((select ... from ...) = 1) then
if (1 = any (select ... from ...)) then
if (1 in (select ... from ...)) then
      

Now, such potentially valid expressions are allowed, removing the need to jump through hoops to fetch the output of a scalar subquery into an intermediate variable using SELECT...INTO.

Tracker reference CORE-2890

(v.2.5.1) SQLSTATE is made available as a PSQL context variable, to be used with WHEN in an exception block, like GDSCODE and SQLCODE.