Make sql query IsNull not work

Hii, I have the next query with left join:

select c.address,, IsNull(b.validate, "No exist") from contracts as c LEFT JOIN cms__bills as b ON

Some rows show me null of course. But IsNull function not working. IFNULL either. How function can I use to replace?

@arturoverbel_bia You are asking how to make an SQL query but this is not really Jet Admin’s area of responsibility, but I will help you, the first link in Google when searching for “Select not null sql query”: SQL NULL Values - IS NULL and IS NOT NULL

Thx! ButI solved on the page. With a custom field. I added a condition value.