Left join and some extra constrain

[Daniel Platz]

Hi,
Even though I don't think this is a Newbie-Question I'll post it in this subforum.
I have got the problem of not being abled to create a sql-statement that fits my needs:
I have got two tables A(PrimaryKey,data) and B(ForeignKey,Flag,data), where B has a foreign key on the A-Table and some data item "Flag" that can be true or false.
What I want now is basically a left join A |X B, but with some extra constrain: If Flag is true I also would like to have a row filled up with NULL-Values, e.g. (1,'test',NULL,NULL,NULL). Also I dont want this row if there are other rows for this A-Table-Primarykey '1'.

Maybe someone gets it and can help me ;-)

Thanks,
Daniel