Adding an one-out-of-two not null constraint in postgresql

Question

If I have a table in Postgresql:

create table Education (      id                  integer references Profiles(id),     finished            YearValue not null,     started             YearValue,     qualification       text,     schoolName          text,     studiedAt           integer references Organizations(id),     primary key (id) ); 

I need to make a constraint so that either schoolName or studiedAt needs to not be null (one of them has to have information in it).

How do I do this?

Answer 1

You can use a check constraint e.g.

constraint chk_education check (schoolName is not null or studiedAt is not null) 

From the manual:

A check constraint is the most generic constraint type. It allows you to specify that the value in a certain column must satisfy a Boolean (truth-value) expression.

Edit: Alternative to comply with Pithyless' interpretation:

constraint chk_education check ((schoolName is not null and studiedAt is null) or (schoolName is null and studiedAt is not null))