pl/pgsql and controling loops

Hi,

i've read several books extract about controlling loops in postgreSQL under
pl/pgsql and there is something interesting.

once to do a comparison they use :

> IF (ret == 1) THEN ...

once,

> IF (ret = 1) THEN...

so are they both correct ?
comming from .NET/C++ world, usually we use '==' or '!=', so i expect that
correct ones are '==' and '<>'.

moreover, when i check if the returned value "ret_email" from SELECT email
INTO ret_email FROM tmp_newsletterreg WHERE tmp_usr_id = id_session;
i want to check if it is empty or not, so i do IF(ret_email <> '' ) THEN...
but it does not work... every time it enter in the loop, even if it is empty
string.

where is the problem ?

thx.

--
Alain
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Windows XP SP2
PostgreSQL 8.2.4 / MS SQL server 2005
Apache 2.2.4
PHP 5.2.4
C# 2005-2008