1. A method of combining data, the method comprising: receiving at a database server a database command that conforms to a database language and that includes a merge operator, wherein the database command includes, as operands for said merge operator, operands that specify a source data structure and a plurality of destination data structures; executing, within the database server the database command wherein the execution of the database command includes performing the steps of: performing a plurality of merge operations using a single scan of a source data structure, wherein each merge operation is an operation to merge data from the source data structure into a different one of the plurality of destination data structures; wherein each of the source data structure and the plurality of destination data structures is a relational data structure; and wherein each merge operation of the plurality of merge operations includes identifying whether any differences exist between data from the source data structure and data from the destination data structure that corresponds to said each merge operation, and modifying data from the destination data structure that corresponds to said each merge operation based on any identified differences; wherein the method is performed by one or more computing devices.