[magicalhippo]

Can you provide a complete working example? I'm just getting "incorrect syntax near !" with both mssql and sqlanywhere.

    create table #nulltest (a bit null);
    insert into #nulltest(a) values (0),(1);
    insert into #nulltest(a) values (null != null);

[distalzou]

Some SQL dialects don't recognize != and use <> instead

[magicalhippo]

True, I'll blame vacation mode for not catching that one.

However, that doesn't change things, I can't get any of these to parse:

    insert into #nulltest(a) values (1 <> 0);
    insert into #nulltest(a) values (null <> null);
    insert into #nulltest(a) values (true and true);
    insert into #nulltest(a) values (null and null);

So my question remains, how do you insert an UNKNOWN?

The point of me asking is that it was my belief contrary to what was suggested, UNKNOWN is not the same as NULL and, crucially, does not evaluate as NULL.