What proper algorithm can I use to extract parent node and child node from a mutual database table?

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C++

MFC

I got a database table from a server.For example,the table named DepartmentInformation.There saved some department name and sub-department name and sub-sub-sub-department name(like this) in it.Taking an example,"00" stands for the highest class department name,and "01" , "02" ... (like that) are the sub-department of "00", continuing, "0101" is the sub-department name of "01" ,"010101" is the sub-item of "0101" ... (the sub-item's length is longer than its parent's node name,but the header sub-string of sub-item is the same as the parent's) ... they were saved in a mutual table.

But I am afraid that it slow down the speed because of the much amount of data(around 80 thousands).

So what kind of proper algorithm can I take a try? Thanks for answering!

What I have tried:

I use the map data structure to save the table data from the database.I am ready to take the recursion way to extract the parent-item and child-item.First of all,I am going to find the root item in the map by using the recursion algorithm.And then find the sub-item of the root item,like this ...