On Tue, Mar 29, 2016 at 12:38 PM, Pavel Stehule <pavel.stehule@gmail.com> wrote:
> The coalesce is one few functions implemented by special rule in
> PostgreSQL parser.
In the SQL standard the COALESCE feature is not listed as a
function; it is listed as one of the short forms of CASE
expression. While it has function-like syntax, thinking of it as a
function is semantically incorrect.
COALESCE(a, b)
is supposed to be semantically equivalent to:
CASE WHEN a is not null THEN a ELSE b END
Among other things, that means that this statement should not
generate a divide by zero error:
SELECT COALESCE(1, 1/0);
--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company