1. A method of combining data within a relational database system, the method comprising: performing a single scan of a source data structure to obtain source data; performing a first merge operation between a first subset of said source data from said source data structure and data from a first destination data structure to make: a first modification to said first destination data structure, said first modification including first modified data in said first destination data structure, and a first augmentation to said first subset of said source data to reflect said first modified data in said first destination data structure; performing said first merge operation between a second subset of said source data from said source data structure and said data from said first destination data structure to make: a second modification to said first destination data structure, said second modification including second modified data in said first destination data structure, and a second augmentation to said second subset of said source data to reflect said second modified data in said first destination data structure; while performing said first merge operation between said second subset of said source data from said source data structure and said data from said first destination data structure, performing a second merge operation between said first subset of said source data as augmented to reflect said first modification and data from a second destination data structure to make a modification to said second destination data structure; wherein the method is performed by one or more computing devices.