Postgresql, select empty fields

Question

I'm trying to get empty "text" fields from my table which I cleared manually with pgadmin. Initially in those fields was '' and I can query them like this:

SELECT mystr, mystr1 FROM mytable WHERE mystr='' or mystr1=''

But that not work if I delete text from them and leave cells blank.

How to write query to get those '' and clear cells together in result? Or clear cells alone?

Answer 1

SELECT mystr, mystr1 
FROM mytable 
WHERE COALESCE(mystr, '') = '' 
   OR COALESCE(mystr1, '') = ''
    ;

Explanation: the coalesce(a,b,c, ...) function traverses the list a,b,c,... from left to right and stops at the first non-null element. a,b,c can be any expression (or constant), but must yield the same type (or be coercable to the same type).