空值判断

-- 查询为空的 is null,sql简写isnull
select * from employees where manager_id isnull;

select * from employees where manager_id is null;

非空判断

-- 查询不为空的 is not null;sql简写notnull
select * from employees where manager_id is not null;
select * from employees where manager_id notnull;

总结