ERROR: query has no destination for result data

Question

CREATE OR REPLACE FUNCTION _chkLogin(userid varchar, pwd varchar)
RETURNS BOOLEAN AS
$BODY$
DECLARE 
 passed BOOLEAN;
BEGIN
 SELECT  (_password = $2) FROM _vRegistration         


        

Answer 1

Notes about assign value

(see this other question for assign value to variable at declaration section)

The language PLpgSQL syntax have many ways to say:

 Y := f(X);

The EXECUTE clause is only for "dynamic execution" (less performance),

 EXECUTE 'f(X)' INTO Y;     

Use Y := f(X); or SELECT for execute static declarations,

 SELECT f(X) INTO Y;

Use PERFORM statment when discard the results or to work with void returns:

 PERFORM f(X);     

Answer 2

You do return passed but you never assign value to it.

And select command within the function has to have place to put data to.

So. Change your SQL to:

SELECT  (_password = $2) INTO passed FROM _vRegistration WHERE _userid = $1;

Also - since you're using names for variables (userid, pwd) use them:

SELECT  (_password = pwd) INTO passed FROM _vRegistration WHERE _userid = userid;