Oracle has a proprietary family tree feature that allows you to traverse a hierarchy and a family-tree type of report with a single SQL query. This uses the connect by, start with, and prior features. Consider an explosion of a family tree from the root to the leaf levels: Our table will contain the columns parent_column and child_column. These will follow the relationship from great-grandparent to grandparent to parent to child, assuming that the same person can exist as both a parent and a child and that every person exists as a child (though not necessarily as a parent). We will start to build the tree from the oldest person, Adam, and will continue through the succeeding leaf levels in the following manner:

Select parent_column, child_column
>From Family_Tree
start with child_column = 'Adam'
connect by parent_column = PRIOR child_column;

If our table contains the following:

the result below will be returned, indented to show the effect of the hierarchy:

Parent_column   child_column  
Unknown         Adam  
Adam               Steve  
Steve                  Helen  
Adam               Bill  
Bill                   Mary  
Mary                         Ann  


This family tree does not need to be balanced. Notice the keyword  Prior,
which connects a column in a new row to a column in the previously 
selected row.