Question

We have a table with a parent-child relation and would like to get it sorted. The sorting criteria is so that when iterating though the result the row matching a parent ID should already be there :

ID   PARENT_ID 
EF01 EF02         // This is wrong as the row EF02 is after and will fail.
EF02    
BB   AA           // here BB < AA
AA   EF01 

The problem is that both key are string, therefore sorting by ID or PARENT_ID is not going to fix the problem.

Answer 1

For Oracle, using hierarchical queries:

 select id, parent_id, level from the_table
 start with parent_id is null
 connect by prior id = parent_id;