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Microsoft Azure SQL Data Warehouse - Architecture and SQL by Todd Wilson, Tom Coffing

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Chapter 3 – Hashing and Data Distribution

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Distribution Keys Hashed on Unique Values Spread Evenly

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When you have a Distribution Key by Hash and the values in that column are unique, the data will spread perfectly evenly in your Azure SQL Data Warehouse system. This is because the data values in the Hash Key use a hashing formula. The formula is designed to be consistent and spread the data evenly.

Distribution Keys With Non-Unique Values Spread Unevenly

When you have a Distribution Key by Hash and the values in that column are non-unique the data ...

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