db2 - SQL dynamic where clause based on parent table column -

i've below 2 tables , need single sql these requirements (no union).

if check_child false, return rows parent table. if check_child true, check if there reference row in child table , return parent row. if there no reference row in child table, don't return parent row.

  parent table   id           int (pk)   check_child  boolean    child table   id          int (pk)   parent_id   int (fk) 

sample data:

    parent table     ------------     id    check_child     1     false     2     true     3     true      child table     -----------     id    parent_id     1     2 

with sample data, query should return first 2 rows parent table because third row doesn't have reference row in child table.

a couple of alternatives:

select p.*  parent p left outer join child c   on c.parent_id = p.id p.check_child = 'false'    or c.parent_id not null 

or

select *  parent p p.check_child = 'false'    or (     p.check_child = 'true'      , exists (select 1 child c c.parent_id = p.id)    )