CREATE TABLE residents (unprop TEXT, prop TEXT, rodstv TEXT, incode TEXT, passport TEXT, apart TEXT, f TEXT, i TEXT, id INTEGER PRIMARY KEY, o TEXT, year TEXT);

update residents set prop = 0 where prop = ""

update residents set unprop = 0 where unprop = ""

select * from residents where unprop > "" возвращает строки с не пустым значением поля
select * from residents where unprop = "" ничего не возвращает

update residents set prop = 0 where prop = ""

update residents set prop = 0 where prop is null