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Rowset: The Processing Data Structure (U-SQL)

Michael Rys|Last Updated: 5/15/2018
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4 Contributors

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:

  1. A U-SQL rowset flows through the U-SQL expression flow and only gets persisted with an explicit insertion into a table using an INSERT or CREATE TABLE AS statement.

    Note that the variables assigned to rowset expressions are not materializing a rowset. The variables represent names for the rowset expressions.

  2. 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.

  3. U-SQL rows can contain up to 4 MB of data per row.

  4. Each rowset column is named with either a quoted or unquoted identifier and is of one of the supported built-in U-SQL column types.

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