Rowset: The Processing Data Structure (U-SQL)
Since U-SQL is a SQL based language, its main processing data structure is a rowset. Thus any data that needs to be processed needs to be transformed into a rowset first and then combined with other rowsets and transformed with U-SQL query expressions. Here are some U-SQL specific aspects of its rowsets:
Note that the variables assigned to rowset expressions are not materializing a rowset. The variables represent names for the rowset expressions.
A rowset is unordered. This means any order among the rows cannot be relied upon in a subsequent expression. This also means that the ORDER BY clause is only supported in contexts where order is usable. The fact that rowsets are unordered also provides the ability to scale out the processing of a rowset across as many parallel processing nodes as needed.
U-SQL rows can contain up to 4 MB of data per row.