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One such error for Azure SQL Database users employing DataSync is: “Database provisioning failed with the exception ‘Column is of a type that is invalid for use as a key column in an index.” This article aims to dissect this error, providing insights and practical solutions for database administrators and developers.


Understanding the Error:


This error signifies a mismatch between the column data type used in an index and what is permissible within Azure SQL DataSync’s framework. Such mismatches can disrupt database provisioning, a critical step in synchronization processes.


Data Types and Index Restrictions in DataSync:


Azure SQL Data Sync imposes specific limitations on data types and index properties. Notably, it does not support indexes on columns with nvarchar(max)that our customer has. Additionally, primary keys cannot be of types like sql_variant, binary, varbinary, image, and xmlWhat is SQL Data Sync for Azure? – Azure SQL Database | Microsoft Learn


Practical Solutions:


  1. Modify Data Types: If feasible, alter the data type from nvarchar(max) to a smaller variant .

  2. Index Adjustments: Review your database schema and modify or remove indexes that include unsupported column types.

  3. Exclude Problematic Columns: Consider omitting columns with unsupported data types from your DataSync synchronization groups.



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