Much of the business data that we work is hierachical. For example, if we are maintaining a customer list we may be dealing with a large corporation that owns seveal companies. A child company could also be a parent to another company.
Each company is a separate legal and billing entity. However we need to develop meaningful reports to determine how much business we are doing with the whole parent organization. In my example we have a parent organization called General Company. Our goal is to summarize sales for all companies that belong to General Company.
We have created a table called CompanyHierarchy which records the relationships between Companies. There are two fields in the table: ParentCompanyID and CompanyID. The ParentCompanyID field holds the parent company's CompanyID. We might also choose not to use a linkage table-in that case we would create ParentCompanyID field in the Companies table and modify the stored procedures.
The two stored procedures, sp_sumCompanySales and sp_getCompanies, are used to create a temporary table that holds the parent company and all its children's CompanyID records. Once we have this temporary table we can use it to aggregate data. In the example we have built up our company list and then use it to aggregate sales figures.
The procedure sp_sumCompanySales invokes sp_getCompanies to get the list and then performs the aggregation. In the procedure sp_getCompanies we are recursively going down from the parent to the lowest children.
sp_sumCompanySales 1 --summarizes all Companies because Company 1 is the master
sp_sumCompanySales 2 --summarizes all Companies except 1 (the parent) and 3 (a child of 1)
Example Data to import: